cross-stdenv: Only prune most overrides in the final stage

Before all overrides were also pruned in the previous stage, now
only gcc and binutils are, because they alone care about about the
target platform. The rest of the overrides don't, so it's better to
preserve them in order to avoid spurious rebuilds.

pkgs/stdenv/adapters.nix

@@ -58,6 +58,10 @@ rec {
   # builds.
   makeStdenvCross = stdenv: cross: binutilsCross: gccCross: stdenv // {
 
+    # Overrides are surely not valid as packages built with this run on a
+    # different platform.
+    overrides = _: _: {};
+
     mkDerivation =
       { name ? "", buildInputs ? [], nativeBuildInputs ? []
       , propagatedBuildInputs ? [], propagatedNativeBuildInputs ? []

pkgs/stdenv/cross/default.nix

@@ -21,9 +21,7 @@ in bootStages ++ [
     selfBuild = false;
     # It's OK to change the built-time dependencies
     allowCustomOverrides = true;
-    stdenv = vanillaPackages.stdenv // {
-      overrides = _: _: {};
-    };
+    inherit (vanillaPackages) stdenv;
   })
 
   # Run Packages

pkgs/stdenv/darwin/default.nix

@@ -253,7 +253,7 @@ in rec {
     inherit
       gnumake gzip gnused bzip2 gawk ed xz patch bash
       libcxxabi libcxx ncurses libffi zlib icu llvm gmp pcre gnugrep
-      coreutils findutils diffutils patchutils binutils binutils-raw;
+      coreutils findutils diffutils patchutils;
 
     llvmPackages = super.llvmPackages // {
       inherit (llvmPackages) llvm clang-unwrapped;
@@ -262,6 +262,9 @@ in rec {
     darwin = super.darwin // {
       inherit (darwin) dyld Libsystem cctools libiconv;
     };
+  } // lib.optionalAttrs (super.targetPlatform == localSystem) {
+    # Need to get rid of these when cross-compiling.
+    inherit binutils binutils-raw;
   };
 
   stdenvDarwin = prevStage: let pkgs = prevStage; in import ../generic rec {

pkgs/stdenv/linux/default.nix

@@ -298,12 +298,14 @@ in
         */
 
       overrides = self: super: {
-        gcc = cc;
-
         inherit (prevStage)
-          gzip bzip2 xz bash binutils coreutils diffutils findutils gawk
+          gzip bzip2 xz bash coreutils diffutils findutils gawk
           glibc gnumake gnused gnutar gnugrep gnupatch patchelf
           attr acl paxctl zlib pcre;
+      } // lib.optionalAttrs (super.targetPlatform == localSystem) {
+        # Need to get rid of these when cross-compiling.
+        inherit (prevStage) binutils;
+        gcc = cc;
       };
     };
   })