cc-wrapper: wrap TOOL and ${targetPrefix}-TOOL if both exist

In NixOS#87909 ("stdenv: always
pass --build, --host to configure") we noticed that stdenv.cc
exposes `c++` as a wrapped bianry and `x86_64-unknown-linux-gnu-c++`
as unsrapped binary.

As a result `x86_64-unknown-linux-gnu-c++` was not able to create
basic bianries. This makes seepingly no-op `--host=x86_64-unknown-linux-gnu`
option for `./configure` a breaking change.

This change adds wrappers to prefixed binaries for cross and
native cases where such an inconsistency exists. New validation
change will catch new possible inconsistencies. It already caught
existing inconsistencies in: `gcc`, `gfortran`, `gcj`, `gccgo`, `gdc`,
`clang`.

At least `radare2` build is fixed by consistent wrappers. It used to fail
before as:

    radare2> ERROR: x86_64-unknown-linux-gnu-gcc cannot create executables

Issue: NixOS#178802

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

@@ -38,6 +38,7 @@ let
   # default.
   targetPrefix = lib.optionalString (targetPlatform != hostPlatform)
                                            (targetPlatform.config + "-");
+  targetPrefixForSure = targetPlatform.config + "-";
 
   ccVersion = lib.getVersion cc;
   ccName = lib.removePrefix targetPrefix (lib.getName cc);
@@ -182,8 +183,11 @@ stdenv.mkDerivation {
         substituteAll "$wrapper" "$out/bin/$dst"
         chmod +x "$out/bin/$dst"
       }
-    ''
 
+      # We collect here all the wrappers needed to be created
+      # to get consistent prefixed and unprefixed coverage.
+      wrap_if_needed=()
+    ''
     + (if nativeTools then ''
       echo ${if targetPlatform.isDarwin then cc else nativePrefix} > $out/nix-support/orig-cc
 
@@ -210,26 +214,31 @@ stdenv.mkDerivation {
       export named_cxx=${targetPrefix}c++
 
       if [ -e $ccPath/${targetPrefix}gcc ]; then
+        wrap_if_needed+=(gcc)
         wrap ${targetPrefix}gcc $wrapper $ccPath/${targetPrefix}gcc
         ln -s ${targetPrefix}gcc $out/bin/${targetPrefix}cc
         export named_cc=${targetPrefix}gcc
         export named_cxx=${targetPrefix}g++
       elif [ -e $ccPath/clang ]; then
+        wrap_if_needed+=(clang)
         wrap ${targetPrefix}clang $wrapper $ccPath/clang
         ln -s ${targetPrefix}clang $out/bin/${targetPrefix}cc
         export named_cc=${targetPrefix}clang
         export named_cxx=${targetPrefix}clang++
       fi
 
       if [ -e $ccPath/${targetPrefix}g++ ]; then
+        wrap_if_needed+=(g++ c++)
         wrap ${targetPrefix}g++ $wrapper $ccPath/${targetPrefix}g++
         ln -s ${targetPrefix}g++ $out/bin/${targetPrefix}c++
       elif [ -e $ccPath/clang++ ]; then
+        wrap_if_needed+=(clang++)
         wrap ${targetPrefix}clang++ $wrapper $ccPath/clang++
         ln -s ${targetPrefix}clang++ $out/bin/${targetPrefix}c++
       fi
 
       if [ -e $ccPath/cpp ]; then
+        wrap_if_needed+=(cpp)
         wrap ${targetPrefix}cpp $wrapper $ccPath/cpp
       fi
     ''
@@ -246,22 +255,92 @@ stdenv.mkDerivation {
     ''
 
     + optionalString cc.langD or false ''
+      wrap_if_needed+=(gdc)
       wrap ${targetPrefix}gdc $wrapper $ccPath/${targetPrefix}gdc
     ''
 
     + optionalString cc.langFortran or false ''
+      wrap_if_needed+=(gfortran)
       wrap ${targetPrefix}gfortran $wrapper $ccPath/${targetPrefix}gfortran
       ln -sv ${targetPrefix}gfortran $out/bin/${targetPrefix}g77
       ln -sv ${targetPrefix}gfortran $out/bin/${targetPrefix}f77
       export named_fc=${targetPrefix}gfortran
     ''
 
     + optionalString cc.langJava or false ''
+      wrap_if_needed+=(gcj)
       wrap ${targetPrefix}gcj $wrapper $ccPath/${targetPrefix}gcj
     ''
 
     + optionalString cc.langGo or false ''
+      wrap_if_needed+=(gccgo)
       wrap ${targetPrefix}gccgo $wrapper $ccPath/${targetPrefix}gccgo
+    ''
+
+    + ''
+      # Can be removed once/if we stop installing unprefixed tools.
+      # Meanwhile make sure both $TOOL and $targetPrefixForSure$TOOL
+      # are both overridden. We also validate for inconsistencies
+      # slightly below.
+      for tool in "''${wrap_if_needed[@]}"; do
+        if [ -e $ccPath/$tool -a ! -e $out/bin/$tool ]; then
+          wrap $tool $wrapper $ccPath/$tool
+        fi
+        if [ -e $ccPath/${targetPrefixForSure}$tool -a ! -e $out/bin/${targetPrefixForSure}$tool ]; then
+          wrap ${targetPrefixForSure}$tool $wrapper $ccPath/${targetPrefixForSure}$tool
+        fi
+      done
+
+      # Validate that all $TOOL wrappers present in $out/bin cover
+      # both $ccPath/$TOOL and $ccPath/$targetPrefixForSure-$TOOL.
+      # Otherwise we get an inconsistency when we expose both wrapped
+      # and unwrapped tool with and without prefix:
+      #   https://github.com/NixOS/nixpkgs/issues/178802
+
+      validate_wrapped() {
+        local maybe_prefixed_bin=$1
+        # 'c++' or 'x86_64-unknown-linux-gnu-c++' -> 'c++'
+        local bin=''${maybe_prefixed_bin#${targetPrefixForSure}}
+        local prefixed_bin=${targetPrefixForSure}$bin
+
+        # Make sure possible unprefixed tool is covered as unprefixed.
+        # Example inconsistency:
+        #   $ccPath:  c++
+        #   $out/bin: foo-c++
+        if [ -e $ccPath/$bin -a -e $out/bin/$prefixed_bin ]; then
+          if [ ! -e $out/bin/$bin ]; then
+            echo "ERROR: '$bin' compiler tool is not overridden by wrapper:"
+            echo "  https://github.com/NixOS/nixpkgs/issues/178802"
+            echo "ccPath binaries:"
+            ls $ccPath
+            echo "wrapped binaries:"
+            ls $out/bin
+            exit 1
+          fi
+        fi
+
+        # Make sure possible prefixed tool is covered as prefixed.
+        # Example inconsistency:
+        #   $ccPath: foo-c++
+        #   $out/bin: c++
+        if [ -e $ccPath/$prefixed_bin -a -e $out/bin/$bin ]; then
+          if [ ! -e $out/bin/$prefixed_bin ]; then
+            echo "ERROR: '$prefixed_bin' compiler tool is not overridden by wrapper:"
+            echo "  https://github.com/NixOS/nixpkgs/issues/178802"
+            echo "ccPath binaries:"
+            ls $ccPath
+            echo "wrapped binaries:"
+            ls $out/bin
+            exit 1
+          fi
+        fi
+      }
+
+      pushd $out/bin
+        for wrapped in *; do
+          validate_wrapped "$wrapped"
+        done
+      popd
     '';
 
   strictDeps = true;