treewide: Get rid of `cc.gcc`

Instead, we have a new `gccForLibs`, which has the appropriate
definition for e.g. avoiding `x86_32` linking problems.

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

@@ -8,6 +8,7 @@
 { name ? ""
 , stdenvNoCC
 , cc ? null, libc ? null, bintools, coreutils ? null, shell ? stdenvNoCC.shell
+, gccForLibs ? null
 , zlib ? null
 , nativeTools, noLibc ? false, nativeLibc, nativePrefix ? ""
 , propagateDoc ? cc != null && cc ? man
@@ -262,11 +263,11 @@ stdenv.mkDerivation {
     ##
     ## GCC libs for non-GCC support
     ##
-    + optionalString (isClang && libcxx == null && cc ? gcc) ''
+    + optionalString (isClang && libcxx == null && !(stdenv.targetPlatform.useLLVM or false) && gccForLibs != null) ''
 
-      echo "-B${cc.gcc}/lib/gcc/${targetPlatform.config}/${cc.gcc.version}" >> $out/nix-support/cc-cflags
-      echo "-L${cc.gcc}/lib/gcc/${targetPlatform.config}/${cc.gcc.version}" >> $out/nix-support/cc-ldflags
-      echo "-L${cc.gcc.lib}/${targetPlatform.config}/lib" >> $out/nix-support/cc-ldflags
+      echo "-B${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
     ''
 
     ##
@@ -306,14 +307,15 @@ stdenv.mkDerivation {
 
     # We have a libc++ directly, we have one via "smuggled" GCC, or we have one
     # bundled with the C compiler because it is GCC
-    + optionalString (libcxx != null || cc.gcc.langCC or false || (isGNU && cc.langCC or false)) ''
+    + optionalString (libcxx != null || (isClang && !(stdenv.targetPlatform.useLLVM or false) && gccForLibs.langCC or false) || (isGNU && cc.langCC or false)) ''
       touch "$out/nix-support/libcxx-cxxflags"
       touch "$out/nix-support/libcxx-ldflags"
-    '' + optionalString (libcxx == null && cc ? gcc) ''
-      for dir in ${cc.gcc}/include/c++/*; do
+    ''
+    + optionalString (libcxx == null && (isClang && !(stdenv.targetPlatform.useLLVM or false) && gccForLibs.langCC or false)) ''
+      for dir in ${gccForLibs}/include/c++/*; do
         echo "-isystem $dir" >> $out/nix-support/libcxx-cxxflags
       done
-      for dir in ${cc.gcc}/include/c++/*/${targetPlatform.config}; do
+      for dir in ${gccForLibs}/include/c++/*/${targetPlatform.config}; do
         echo "-isystem $dir" >> $out/nix-support/libcxx-cxxflags
       done
     ''

pkgs/development/compilers/computecpp/default.nix

@@ -37,8 +37,6 @@ stdenv.mkDerivation rec {
 
   passthru = {
     isClang = true;
-  } // stdenv.lib.optionalAttrs (stdenv.targetPlatform.isLinux || (stdenv.cc.isGNU && stdenv.cc.cc ? gcc)) {
-    gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
   };
 
   meta = with stdenv.lib; {

pkgs/development/compilers/emscripten/fastcomp/emscripten-fastcomp.nix

@@ -1,9 +1,7 @@
-{ emscriptenVersion, stdenv, fetchFromGitHub, cmake, python, gtest, ... }:
+{ emscriptenVersion, stdenv, fetchFromGitHub, cmake, python, gtest, gccForLibs, ... }:
 
 let
   rev = emscriptenVersion;
-  haveGcc = stdenv.cc.isGNU || stdenv.cc.cc ? gcc;
-  gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
 in
 stdenv.mkDerivation rec {
   name = "emscripten-fastcomp-${rev}";
@@ -35,16 +33,14 @@ stdenv.mkDerivation rec {
     #"-DLLVM_CONFIG=${llvm}/bin/llvm-config"
     "-DLLVM_BUILD_TESTS=ON"
     "-DCLANG_INCLUDE_TESTS=ON"
-  ] ++ (stdenv.lib.optional (stdenv.isLinux && haveGcc)
+  ] ++ (stdenv.lib.optional stdenv.isLinux
     # necessary for clang to find crtend.o
-    "-DGCC_INSTALL_PREFIX=${gcc}"
+    "-DGCC_INSTALL_PREFIX=${gccForLibs}"
   );
   enableParallelBuilding = true;
 
   passthru = {
     isClang = true;
-  } // stdenv.lib.optionalAttrs haveGcc {
-    inherit gcc;
   };
 
   meta = with stdenv.lib; {

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

@@ -86,8 +86,6 @@ let
     passthru = {
       isClang = true;
       inherit llvm;
-    } // stdenv.lib.optionalAttrs (stdenv.targetPlatform.isLinux || (stdenv.cc.isGNU && stdenv.cc.cc ? gcc)) {
-      gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
     };
 
     meta = {

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

@@ -1,5 +1,6 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake
+{ lowPrio, newScope, pkgs, stdenv, cmake, gccForLibs
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
+, buildPackages
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
 }:
@@ -24,8 +25,8 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 
@@ -59,7 +60,8 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];

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

@@ -4,7 +4,6 @@
 }:
 
 let
-  gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
   self = stdenv.mkDerivation ({
     pname = "clang";
     inherit version;
@@ -77,8 +76,6 @@ let
     passthru = {
       isClang = true;
       inherit llvm;
-    } // stdenv.lib.optionalAttrs stdenv.isLinux {
-      inherit gcc;
     };
 
     meta = {

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

@@ -1,5 +1,6 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake
+{ lowPrio, newScope, pkgs, stdenv, cmake, gccForLibs
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith
+, buildPackages
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
 }:
@@ -24,8 +25,8 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 
@@ -51,7 +52,8 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];

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

@@ -4,7 +4,6 @@
 }:
 
 let
-  gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
   self = stdenv.mkDerivation ({
     pname = "clang";
     inherit version;
@@ -77,8 +76,6 @@ let
     passthru = {
       isClang = true;
       inherit llvm;
-    } // stdenv.lib.optionalAttrs stdenv.targetPlatform.isLinux {
-      inherit gcc;
     };
 
     meta = {

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

@@ -1,5 +1,6 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake
+{ lowPrio, newScope, pkgs, stdenv, cmake, gccForLibs
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith
+, buildPackages
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
 }:
@@ -24,8 +25,8 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 
@@ -51,7 +52,8 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];

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

@@ -87,8 +87,6 @@ let
     passthru = {
       isClang = true;
       inherit llvm;
-    } // stdenv.lib.optionalAttrs (stdenv.targetPlatform.isLinux || (stdenv.cc.isGNU && stdenv.cc.cc ? gcc)) {
-      gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
     };
 
     meta = {

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

@@ -1,5 +1,6 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake
+{ lowPrio, newScope, pkgs, stdenv, cmake, gccForLibs
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
+, buildPackages
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
 }:
@@ -24,8 +25,8 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 
@@ -58,7 +59,8 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];

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

@@ -97,8 +97,6 @@ let
     passthru = {
       isClang = true;
       inherit llvm;
-    } // stdenv.lib.optionalAttrs (stdenv.targetPlatform.isLinux || (stdenv.cc.isGNU && stdenv.cc.cc ? gcc)) {
-      gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
     };
 
     meta = {

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

@@ -1,5 +1,6 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake
+{ lowPrio, newScope, pkgs, stdenv, cmake, gccForLibs
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
+, buildPackages
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
 }:
@@ -24,8 +25,8 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 
@@ -59,7 +60,8 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];

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

@@ -92,8 +92,6 @@ let
     passthru = {
       isClang = true;
       inherit llvm;
-    } // stdenv.lib.optionalAttrs (stdenv.targetPlatform.isLinux || (stdenv.cc.isGNU && stdenv.cc.cc ? gcc)) {
-      gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
     };
 
     meta = {

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

@@ -1,5 +1,6 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake
+{ lowPrio, newScope, pkgs, stdenv, cmake, gccForLibs
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
+, buildPackages
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
 }:
@@ -24,8 +25,8 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   in {
 
@@ -59,7 +60,8 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];

pkgs/development/compilers/swift/default.nix

@@ -2,6 +2,7 @@
 , cmake
 , coreutils
 , glibc
+, gccForLibs
 , which
 , perl
 , libedit
@@ -121,7 +122,7 @@ let
   cmakeFlags = [
     "-DGLIBC_INCLUDE_PATH=${stdenv.cc.libc.dev}/include"
     "-DC_INCLUDE_DIRS=${stdenv.lib.makeSearchPathOutput "dev" "include" devInputs}:${libxml2.dev}/include/libxml2"
-    "-DGCC_INSTALL_PREFIX=${clang.cc.gcc}"
+    "-DGCC_INSTALL_PREFIX=${gccForLibs}"
   ];
 
 in
@@ -199,7 +200,7 @@ stdenv.mkDerivation {
     substituteInPlace swift/stdlib/public/Platform/CMakeLists.txt \
       --replace '/usr/include' "${stdenv.cc.libc.dev}/include"
     substituteInPlace swift/utils/build-script-impl \
-      --replace '/usr/include/c++' "${clang.cc.gcc}/include/c++"
+      --replace '/usr/include/c++' "${gccForLibs}/include/c++"
     patch -p1 -d swift -i ${./patches/glibc-arch-headers.patch}
     patch -p1 -d swift -i ${./patches/0001-build-presets-linux-don-t-require-using-Ninja.patch}
     patch -p1 -d swift -i ${./patches/0002-build-presets-linux-allow-custom-install-prefix.patch}
@@ -264,7 +265,7 @@ stdenv.mkDerivation {
     export NIX_CFLAGS_COMPILE="$(< $NIX_CC/nix-support/libcxx-cxxflags) $NIX_CFLAGS_COMPILE"
     # During the Swift build, a full local LLVM build is performed and the resulting clang is invoked.
     # This compiler is not using the Nix wrappers, so it needs some help to find things.
-    export NIX_LDFLAGS_BEFORE="-rpath ${clang.cc.gcc.lib}/lib -L${clang.cc.gcc.lib}/lib $NIX_LDFLAGS_BEFORE"
+    export NIX_LDFLAGS_BEFORE="-rpath ${gccForLibs.lib}/lib -L${gccForLibs.lib}/lib $NIX_LDFLAGS_BEFORE"
     # However, we want to use the wrapped compiler whenever possible.
     export CC="${clang}/bin/clang"
 

pkgs/top-level/all-packages.nix

@@ -8319,8 +8319,8 @@ in
       mkdir -p "$rsrc/lib"
       ln -s "${cc}/lib" "$rsrc/include"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && cc ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
-      echo "--gcc-toolchain=${cc.gcc}" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
     '';
   };
 
@@ -9112,55 +9112,41 @@ in
 
   llvmPackages = recurseIntoAttrs llvmPackages_7;
 
-  llvmPackages_5 = callPackage ../development/compilers/llvm/5 ({
+  llvmPackages_5 = callPackage ../development/compilers/llvm/5 {
     inherit (stdenvAdapters) overrideCC;
     buildLlvmTools = buildPackages.llvmPackages_5.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_5.libraries;
-  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && stdenv.cc.isGNU) {
-    stdenv = gcc6Stdenv; # with gcc-7: undefined reference to `__divmoddi4'
-  });
+  };
 
-  llvmPackages_6 = callPackage ../development/compilers/llvm/6 ({
+  llvmPackages_6 = callPackage ../development/compilers/llvm/6 {
     inherit (stdenvAdapters) overrideCC;
     buildLlvmTools = buildPackages.llvmPackages_6.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_6.libraries;
-  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && stdenv.cc.isGNU) {
-    # with gcc-7 on i686: undefined reference to `__divmoddi4'
-    # Failing tests with gcc8.
-    stdenv = overrideCC stdenv (if stdenv.hostPlatform.isi686 then gcc6 else gcc7);
-  });
+  };
 
-  llvmPackages_7 = callPackage ../development/compilers/llvm/7 ({
+  llvmPackages_7 = callPackage ../development/compilers/llvm/7 {
     inherit (stdenvAdapters) overrideCC;
     buildLlvmTools = buildPackages.llvmPackages_7.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_7.libraries;
-  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && buildPackages.stdenv.cc.isGNU) {
-    stdenv = gcc6Stdenv; # with gcc-7: undefined reference to `__divmoddi4'
-  });
+  };
 
-  llvmPackages_8 = callPackage ../development/compilers/llvm/8 ({
+  llvmPackages_8 = callPackage ../development/compilers/llvm/8 {
     inherit (stdenvAdapters) overrideCC;
     buildLlvmTools = buildPackages.llvmPackages_8.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_8.libraries;
-  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && buildPackages.stdenv.cc.isGNU) {
-    stdenv = gcc6Stdenv; # with gcc-7: undefined reference to `__divmoddi4'
-  });
+  };
 
-  llvmPackages_9 = callPackage ../development/compilers/llvm/9 ({
+  llvmPackages_9 = callPackage ../development/compilers/llvm/9 {
     inherit (stdenvAdapters) overrideCC;
     buildLlvmTools = buildPackages.llvmPackages_9.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_9.libraries;
-  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && buildPackages.stdenv.cc.isGNU) {
-    stdenv = gcc6Stdenv; # with gcc-7: undefined reference to `__divmoddi4'
-  });
+  };
 
-  llvmPackages_10 = callPackage ../development/compilers/llvm/10 ({
+  llvmPackages_10 = callPackage ../development/compilers/llvm/10 {
     inherit (stdenvAdapters) overrideCC;
     buildLlvmTools = buildPackages.llvmPackages_10.tools;
     targetLlvmLibraries = targetPackages.llvmPackages_10.libraries;
-  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && buildPackages.stdenv.cc.isGNU) {
-    stdenv = gcc7Stdenv;
-  });
+  };
 
   llvmPackages_latest = llvmPackages_10;
 
@@ -10496,6 +10482,17 @@ in
     stdenvNoLibs = gccStdenvNoLibs; # cannot be built with clang it seems
   };
 
+  # This is for e.g. LLVM libraries on linux.
+  gccForLibs =
+    # with gcc-7: undefined reference to `__divmoddi4'
+    if stdenv.targetPlatform.isi686
+      then gcc6.cc
+    else if stdenv.targetPlatform == stdenv.hostPlatform && targetPackages.stdenv.cc.isGNU
+	  # Can only do this is in the native case, otherwise we might get infinite
+	  # recursion if `targetPackages.stdenv.cc.cc` itself uses `gccForLibs`.
+      then targetPackages.stdenv.cc.cc
+    else gcc.cc;
+
   libstdcxx5 = callPackage ../development/libraries/gcc/libstdc++/5.nix { };
 
   libsigrok = callPackage ../development/tools/libsigrok { };