llvmPackages.compiler-rt: Backported X86 support

patch from LLVM11

pkgs/development/compilers/llvm/10/compiler-rt/X86-support-extension.patch

@@ -0,0 +1,23 @@
+diff --git a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
+index 3a66dd9c3fb..7efc85d9f9f 100644
+--- a/lib/builtins/CMakeLists.txt
++++ b/lib/builtins/CMakeLists.txt
+@@ -301,6 +301,10 @@ if (NOT MSVC)
+     i386/umoddi3.S
+   )
+ 
++  set(i486_SOURCES ${i386_SOURCES})
++  set(i586_SOURCES ${i386_SOURCES})
++  set(i686_SOURCES ${i386_SOURCES})
++
+   if (WIN32)
+     set(i386_SOURCES
+       ${i386_SOURCES}
+@@ -608,6 +612,7 @@ else ()
+   endif()
+ 
+   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
++      message("arch: ${arch}")
+     if (CAN_TARGET_${arch})
+       # For ARM archs, exclude any VFP builtins if VFP is not supported
+       if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em)$")

pkgs/development/compilers/llvm/10/compiler-rt/default.nix

@@ -56,6 +56,7 @@ stdenv.mkDerivation {
     ./find-darwin-sdk-version.patch # don't test for macOS being >= 10.15
     ./gnu-install-dirs.patch
     ../../common/compiler-rt/libsanitizer-no-cyclades-11.patch
+    ./X86-support-extension.patch # backported from LLVM 11
   ] ++ 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