clang, cc-wrapper: Move `--gcc-toolchain` logic into CC wrapper

pkgs/build-support/cc-wrapper/default.nix

@@ -278,12 +278,25 @@ stdenv.mkDerivation {
     ##
     ## GCC libs for non-GCC support
     ##
-    + optionalString useGccForLibs ''
+    + optionalString useGccForLibs (''
 
+    ''
+    # In theory we shouldn't need this, because we always set `useLLVM` on
+    # Darwin, and maybe also break down `useLLVM` into fine-grained use flags
+    # (libgcc vs compiler-rt, ld.lld vs legacy, libc++ vs libstdc++, etc.)
+    # since Darwin isn't `useLLVM` on all counts. (See
+    # https://clang.llvm.org/docs/Toolchain.html for all the axes one might
+    # break `useLLVM` into.)
+    #
+    # But, for now, we haven't doneo these things, so we use
+    # `targetPlatform.isLinux` as a proxy.
+    + optionalString targetPlatform.isLinux ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
+    '' + ''
       echo "-B${gccForLibs}/lib/gcc/${targetPlatform.config}/${gccForLibs.version}" >> $out/nix-support/cc-cflags
       echo "-L${gccForLibs}/lib/gcc/${targetPlatform.config}/${gccForLibs.version}" >> $out/nix-support/cc-ldflags
       echo "-L${gccForLibs.lib}/${targetPlatform.config}/lib" >> $out/nix-support/cc-ldflags
-    ''
+    '')
 
     ##
     ## General libc support

pkgs/development/compilers/llvm/10/default.nix

@@ -26,8 +26,6 @@ let
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/share" "$rsrc/share"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/development/compilers/llvm/11/default.nix

@@ -26,8 +26,6 @@ let
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/share" "$rsrc/share"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/development/compilers/llvm/5/default.nix

@@ -25,8 +25,6 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/development/compilers/llvm/6/default.nix

@@ -25,8 +25,6 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/development/compilers/llvm/7/default.nix

@@ -25,8 +25,6 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/development/compilers/llvm/8/default.nix

@@ -25,8 +25,6 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/development/compilers/llvm/9/default.nix

@@ -25,8 +25,6 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 

pkgs/top-level/all-packages.nix

@@ -8853,8 +8853,6 @@ in
       mkdir -p "$rsrc/lib"
       ln -s "${cc}/lib" "$rsrc/include"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   };