diff --git a/pkgs/development/compilers/llvm/10/bintools.nix b/pkgs/development/compilers/llvm/10/bintools/default.nix
similarity index 100%
rename from pkgs/development/compilers/llvm/10/bintools.nix
rename to pkgs/development/compilers/llvm/10/bintools/default.nix
diff --git a/pkgs/development/compilers/llvm/10/compiler-rt/default.nix b/pkgs/development/compilers/llvm/10/compiler-rt/default.nix
index 1f990ac433d2..85f2298f586a 100644
--- a/pkgs/development/compilers/llvm/10/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/10/compiler-rt/default.nix
@@ -4,14 +4,15 @@ let
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
-stdenv.mkDerivation rec {
-  pname = "compiler-rt";
+stdenv.mkDerivation {
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
-  src = fetch pname "1yjqjri753w0fzmxcyz687nvd97sbc9rsqrxzpq720na47hwh3fr";
+  src = fetch "compiler-rt" "1yjqjri753w0fzmxcyz687nvd97sbc9rsqrxzpq720na47hwh3fr";
 
   nativeBuildInputs = [ cmake python3 llvm.dev ];
   buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
@@ -29,14 +30,15 @@ stdenv.mkDerivation rec {
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
@@ -58,7 +60,6 @@ stdenv.mkDerivation rec {
   ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
     ++ lib.optional stdenv.hostPlatform.isAarch32 ./armv7l.patch;
 
-
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
@@ -88,5 +89,4 @@ stdenv.mkDerivation rec {
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
     ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }
diff --git a/pkgs/development/compilers/llvm/10/default.nix b/pkgs/development/compilers/llvm/10/default.nix
index 754c8cdc7789..ead6c252651b 100644
--- a/pkgs/development/compilers/llvm/10/default.nix
+++ b/pkgs/development/compilers/llvm/10/default.nix
@@ -1,4 +1,5 @@
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@@ -93,7 +94,16 @@ let
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
@@ -112,6 +122,8 @@ let
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
@@ -120,9 +132,7 @@ let
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -136,10 +146,7 @@ let
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -152,26 +159,43 @@ let
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 
diff --git a/pkgs/development/compilers/llvm/11/bintools.nix b/pkgs/development/compilers/llvm/11/bintools/default.nix
similarity index 100%
rename from pkgs/development/compilers/llvm/11/bintools.nix
rename to pkgs/development/compilers/llvm/11/bintools/default.nix
diff --git a/pkgs/development/compilers/llvm/11/compiler-rt/default.nix b/pkgs/development/compilers/llvm/11/compiler-rt/default.nix
index 257bc34092fe..61ff00cda6db 100644
--- a/pkgs/development/compilers/llvm/11/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/11/compiler-rt/default.nix
@@ -4,14 +4,15 @@ let
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
-stdenv.mkDerivation rec {
-  pname = "compiler-rt";
+stdenv.mkDerivation {
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
-  src = fetch pname "0x1j8ngf1zj63wlnns9vlibafq48qcm72p4jpaxkmkb4qw0grwfy";
+  src = fetch "compiler-rt" "0x1j8ngf1zj63wlnns9vlibafq48qcm72p4jpaxkmkb4qw0grwfy";
 
   nativeBuildInputs = [ cmake python3 llvm.dev ];
   buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
@@ -29,14 +30,15 @@ stdenv.mkDerivation rec {
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
@@ -59,7 +61,6 @@ stdenv.mkDerivation rec {
   ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
     ++ lib.optional stdenv.hostPlatform.isAarch32 ./armv7l.patch;
 
-
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
@@ -91,5 +92,4 @@ stdenv.mkDerivation rec {
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
     ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }
diff --git a/pkgs/development/compilers/llvm/11/default.nix b/pkgs/development/compilers/llvm/11/default.nix
index a8f6523dd905..bab5831e17cf 100644
--- a/pkgs/development/compilers/llvm/11/default.nix
+++ b/pkgs/development/compilers/llvm/11/default.nix
@@ -1,4 +1,5 @@
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@@ -94,7 +95,16 @@ let
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
@@ -113,6 +123,8 @@ let
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
@@ -121,9 +133,7 @@ let
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -137,10 +147,7 @@ let
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -153,26 +160,43 @@ let
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 
diff --git a/pkgs/development/compilers/llvm/12/compiler-rt/default.nix b/pkgs/development/compilers/llvm/12/compiler-rt/default.nix
index 8ca01e44a548..895af8f2f020 100644
--- a/pkgs/development/compilers/llvm/12/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/12/compiler-rt/default.nix
@@ -9,7 +9,7 @@ let
 
 in
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation {
   pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
   src = fetch "compiler-rt" "0d444qihq9jhqnfv003cr704v363va72zl6qaw2algj1c85cva45";
@@ -61,7 +61,6 @@ stdenv.mkDerivation rec {
   ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
     ++ lib.optional stdenv.hostPlatform.isAarch32 ./armv7l.patch;
 
-
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
diff --git a/pkgs/development/compilers/llvm/12/default.nix b/pkgs/development/compilers/llvm/12/default.nix
index 73a8b7a90a0e..2d3c1795bd2e 100644
--- a/pkgs/development/compilers/llvm/12/default.nix
+++ b/pkgs/development/compilers/llvm/12/default.nix
@@ -1,4 +1,5 @@
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@@ -112,7 +113,16 @@ let
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
@@ -141,9 +151,7 @@ let
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -157,10 +165,7 @@ let
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -173,10 +178,7 @@ let
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
@@ -186,9 +188,7 @@ let
     lldClangNoCompilerRtWithLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [ ];
       extraBuildCommands = mkExtraBuildCommands0 cc;
     };
@@ -199,15 +199,19 @@ let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt-libc = callPackage ./compiler-rt ({ inherit llvm_meta; } //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      inherit llvm_meta;
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
 
-    compiler-rt-no-libc = callPackage ./compiler-rt ({ inherit llvm_meta; } //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      inherit llvm_meta;
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
 
     # N.B. condition is safe because without useLLVM both are the same.
     compiler-rt = if stdenv.hostPlatform.isAndroid
diff --git a/pkgs/development/compilers/llvm/7/bintools.nix b/pkgs/development/compilers/llvm/7/bintools/default.nix
similarity index 100%
rename from pkgs/development/compilers/llvm/7/bintools.nix
rename to pkgs/development/compilers/llvm/7/bintools/default.nix
diff --git a/pkgs/development/compilers/llvm/7/compiler-rt/default.nix b/pkgs/development/compilers/llvm/7/compiler-rt/default.nix
index 75d61a51e601..d97e54d8f494 100644
--- a/pkgs/development/compilers/llvm/7/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/7/compiler-rt/default.nix
@@ -4,12 +4,13 @@ let
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
 stdenv.mkDerivation {
-  pname = "compiler-rt";
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
   src = fetch "compiler-rt" "1n48p8gjarihkws0i2bay5w9bdwyxyxxbpwyng7ba58jb30dlyq5";
 
@@ -29,14 +30,15 @@ stdenv.mkDerivation {
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
@@ -83,10 +85,9 @@ stdenv.mkDerivation {
   postInstall = lib.optionalString (stdenv.hostPlatform.isDarwin || stdenv.hostPlatform.isWasm) ''
     ln -s "$out/lib"/*/* "$out/lib"
   '' + lib.optionalString (useLLVM) ''
-    ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/linux/crtbegin.o
-    ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/linux/crtend.o
-    ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/linux/crtbeginS.o
-    ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/linux/crtendS.o
+    ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
+    ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
+    ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
+    ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }
diff --git a/pkgs/development/compilers/llvm/7/default.nix b/pkgs/development/compilers/llvm/7/default.nix
index fbae9840b24c..5060777c64a5 100644
--- a/pkgs/development/compilers/llvm/7/default.nix
+++ b/pkgs/development/compilers/llvm/7/default.nix
@@ -1,4 +1,5 @@
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@@ -95,7 +96,16 @@ let
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
@@ -114,6 +124,8 @@ let
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
@@ -122,9 +134,7 @@ let
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -138,10 +148,7 @@ let
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -154,28 +161,44 @@ let
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt {
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
       stdenv = if stdenv.hostPlatform.useLLVM or false
                then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
                else stdenv;
     };
 
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
+
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 
     libcxxStdenv = overrideCC stdenv buildLlvmTools.libcxxClang;
diff --git a/pkgs/development/compilers/llvm/8/bintools.nix b/pkgs/development/compilers/llvm/8/bintools/default.nix
similarity index 100%
rename from pkgs/development/compilers/llvm/8/bintools.nix
rename to pkgs/development/compilers/llvm/8/bintools/default.nix
diff --git a/pkgs/development/compilers/llvm/8/compiler-rt/default.nix b/pkgs/development/compilers/llvm/8/compiler-rt/default.nix
index d370de031bb5..d7d5e36e79df 100644
--- a/pkgs/development/compilers/llvm/8/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/8/compiler-rt/default.nix
@@ -4,12 +4,13 @@ let
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
 stdenv.mkDerivation {
-  pname = "compiler-rt";
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
   src = fetch "compiler-rt" "0dqqf8f930l8gag4d9qjgn1n0pj0nbv2anviqqhdi1rkhas8z0hi";
 
@@ -29,14 +30,15 @@ stdenv.mkDerivation {
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
@@ -88,5 +90,4 @@ stdenv.mkDerivation {
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
     ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }
diff --git a/pkgs/development/compilers/llvm/8/default.nix b/pkgs/development/compilers/llvm/8/default.nix
index ccf80f3df2a8..78deb942c6e1 100644
--- a/pkgs/development/compilers/llvm/8/default.nix
+++ b/pkgs/development/compilers/llvm/8/default.nix
@@ -1,4 +1,5 @@
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@@ -96,7 +97,16 @@ let
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
@@ -115,6 +125,8 @@ let
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
@@ -123,9 +135,7 @@ let
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -139,10 +149,7 @@ let
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -155,26 +162,43 @@ let
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 
diff --git a/pkgs/development/compilers/llvm/9/bintools.nix b/pkgs/development/compilers/llvm/9/bintools/default.nix
similarity index 100%
rename from pkgs/development/compilers/llvm/9/bintools.nix
rename to pkgs/development/compilers/llvm/9/bintools/default.nix
diff --git a/pkgs/development/compilers/llvm/9/compiler-rt/default.nix b/pkgs/development/compilers/llvm/9/compiler-rt/default.nix
index 285fe811514f..def3473a050b 100644
--- a/pkgs/development/compilers/llvm/9/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/9/compiler-rt/default.nix
@@ -4,14 +4,15 @@ let
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
-stdenv.mkDerivation rec {
-  pname = "compiler-rt";
+stdenv.mkDerivation {
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
-  src = fetch pname "0xwh79g3zggdabxgnd0bphry75asm1qz7mv3hcqihqwqr6aspgy2";
+  src = fetch "compiler-rt" "0xwh79g3zggdabxgnd0bphry75asm1qz7mv3hcqihqwqr6aspgy2";
 
   nativeBuildInputs = [ cmake python3 llvm.dev ];
   buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
@@ -29,14 +30,15 @@ stdenv.mkDerivation rec {
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
diff --git a/pkgs/development/compilers/llvm/9/default.nix b/pkgs/development/compilers/llvm/9/default.nix
index ff9a24626306..39b285da2626 100644
--- a/pkgs/development/compilers/llvm/9/default.nix
+++ b/pkgs/development/compilers/llvm/9/default.nix
@@ -1,4 +1,5 @@
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@@ -96,7 +97,16 @@ let
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
@@ -115,6 +125,8 @@ let
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
@@ -123,9 +135,7 @@ let
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -139,10 +149,7 @@ let
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
@@ -155,26 +162,43 @@ let
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index ebedcb0e1682..499dde10f4f9 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -10345,14 +10345,17 @@ in
   gerbil-support = callPackage ../development/compilers/gerbil/gerbil-support.nix { };
   gerbilPackages-unstable = gerbil-support.gerbilPackages-unstable; # NB: don't recurseIntoAttrs for (unstable!) libraries
 
-  gccFun = callPackage (if (with stdenv.targetPlatform; isVc4 || libc == "relibc")
-    then ../development/compilers/gcc/6
-    else ../development/compilers/gcc/10);
-  gcc = if (with stdenv.targetPlatform; isVc4 || libc == "relibc")
-    then gcc6 else
-      # aarch64-darwin doesn't support earlier gcc
-      if (stdenv.targetPlatform.isAarch64 && stdenv.isDarwin) then gcc11
-      else if stdenv.targetPlatform.isAarch64 then gcc9 else gcc10;
+  inherit (let
+      num =
+        if (with stdenv.targetPlatform; isVc4 || libc == "relibc") then 6
+        else if (stdenv.targetPlatform.isAarch64 && stdenv.isDarwin) then 11
+        else if stdenv.targetPlatform.isAarch64 then 9
+        else 10;
+      numS = toString num;
+    in {
+      gcc = pkgs.${"gcc${numS}"};
+      gccFun = callPackage (../development/compilers/gcc + "/${numS}");
+    }) gcc gccFun;
   gcc-unwrapped = gcc.cc;
 
   wrapNonDeterministicGcc = stdenv: ccWrapper:
@@ -10430,7 +10433,7 @@ in
 
   crossLibcStdenv =
     if stdenv.hostPlatform.useLLVM or false
-    then overrideCC stdenv buildPackages.llvmPackages_8.lldClangNoLibc
+    then overrideCC stdenv buildPackages.llvmPackages.lldClangNoLibc
     else gccCrossLibcStdenv;
 
   # The GCC used to build libc for the target platform. Normal gccs will be
@@ -11175,19 +11178,16 @@ in
   llvm_6  = llvmPackages_6.llvm;
   llvm_5  = llvmPackages_5.llvm;
 
-  llvmPackages = with targetPlatform;
-    if isDarwin then
-      llvmPackages_7
-    else if isFreeBSD then
-      llvmPackages_7
-    else if isAndroid then
-      llvmPackages_12
-    else if isLinux then
-      llvmPackages_7
-    else if isWasm then
-      llvmPackages_8
-    else
-      llvmPackages_latest;
+  llvmPackages = let
+    choose = platform:
+      /**/ if platform.isDarwin then "7"
+      else if platform.isFreeBSD then "7"
+      else if platform.isAndroid then "12"
+      else if platform.isLinux then "7"
+      else if platform.isWasm then "8"
+      else "latest";
+    minSupported = lib.min (choose stdenv.hostPlatform) (choose stdenv.targetPlatform);
+  in pkgs.${"llvmPackages_${minSupported}"};
 
   llvmPackages_5 = recurseIntoAttrs (callPackage ../development/compilers/llvm/5 {
     inherit (stdenvAdapters) overrideCC;
@@ -12602,11 +12602,7 @@ in
   });
   binutilsNoLibc = wrapBintoolsWith {
     bintools = binutils-unwrapped;
-    libc =
-      /**/ if stdenv.targetPlatform.libc == "msvcrt" then targetPackages.windows.mingw_w64_headers
-      else if stdenv.targetPlatform.libc == "libSystem" then darwin.xcode
-      else if stdenv.targetPlatform.libc == "nblibc" then targetPackages.netbsdCross.headers
-      else null;
+    libc = preLibcCrossHeaders;
   };
 
   bison = callPackage ../development/tools/parsing/bison { };
@@ -14741,6 +14737,13 @@ in
     stdenv = crossLibcStdenv;
   };
 
+  # These are used when buiding compiler-rt / libgcc, prior to building libc.
+  preLibcCrossHeaders = let
+    inherit (stdenv.targetPlatform) libc;
+  in     if libc == "msvcrt" then targetPackages.windows.mingw_w64_headers
+    else if libc == "nblibc" then targetPackages.netbsdCross.headers
+    else null;
+
   # We can choose:
   libcCrossChooser = name:
     # libc is hackily often used from the previous stage. This `or`
@@ -14755,8 +14758,10 @@ in
     else if name == "newlib" then targetPackages.newlibCross or newlibCross
     else if name == "musl" then targetPackages.muslCross or muslCross
     else if name == "msvcrt" then targetPackages.windows.mingw_w64 or windows.mingw_w64
-    else if stdenv.targetPlatform.useiOSPrebuilt then targetPackages.darwin.iosSdkPkgs.libraries or darwin.iosSdkPkgs.libraries
-    else if name == "libSystem" then targetPackages.darwin.xcode
+    else if name == "libSystem" then
+      if stdenv.targetPlatform.useiOSPrebuilt
+      then targetPackages.darwin.iosSdkPkgs.libraries or darwin.iosSdkPkgs.libraries
+      else throw "don't yet have a `targetPackages.darwin.LibsystemCross`"
     else if name == "nblibc" then targetPackages.netbsdCross.libc or netbsdCross.libc
     else if name == "wasilibc" then targetPackages.wasilibc or wasilibc
     else if name == "relibc" then targetPackages.relibc or relibc
diff --git a/pkgs/top-level/darwin-packages.nix b/pkgs/top-level/darwin-packages.nix
index 5275a6f31232..2af799e56460 100644
--- a/pkgs/top-level/darwin-packages.nix
+++ b/pkgs/top-level/darwin-packages.nix
@@ -2,6 +2,7 @@
 , buildPackages, pkgs, targetPackages
 , pkgsBuildBuild, pkgsBuildHost, pkgsBuildTarget, pkgsHostHost, pkgsTargetTarget
 , stdenv, splicePackages, newScope
+, preLibcCrossHeaders
 }:
 
 let
@@ -52,7 +53,7 @@ impure-cmds // apple-source-releases // {
   };
 
   binutilsNoLibc = pkgs.wrapBintoolsWith {
-    libc = null;
+    libc = preLibcCrossHeaders;
     bintools = self.binutils-unwrapped;
   };