cc-wrapper: Allow for override of -target for clang/clang++

This enables users to make use of clang's multi-platform/target support
without having to go through full cross system setup. This is especially useful
for generating bpf object files, I'm not even usre what would a no-userland
cross compile system tuple even look like to even try going that route.

Fixes #176128

pkgs/build-support/cc-wrapper/cc-wrapper.sh

@@ -29,6 +29,7 @@ cc1=0
 cxxInclude=1
 cxxLibrary=1
 cInclude=1
+needsTarget=@needsTarget@
 
 expandResponseParams "$@"
 linkType=$(checkLinkType "${params[@]}")
@@ -46,6 +47,7 @@ while (( "$n" < "$nParams" )); do
         -nostdinc) cInclude=0 cxxInclude=0 ;;
         -nostdinc++) cxxInclude=0 ;;
         -nostdlib) cxxLibrary=0 ;;
+        -target|--target=*) needsTarget=0;;
         -x)
             case "$p2" in
                 *-header) dontLink=1 ;;
@@ -159,6 +161,10 @@ if [ "$dontLink" != 1 ]; then
     export NIX_LINK_TYPE_@suffixSalt@=$linkType
 fi
 
+if [ $needsTarget == 1 ]; then
+    extraAfter+=(-target @defaultTarget@)
+fi
+
 # As a very special hack, if the arguments are just `-v', then don't
 # add anything.  This is to prevent `gcc -v' (which normally prints
 # out the version number and returns exit code 0) from printing out

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

@@ -208,6 +208,7 @@ stdenv.mkDerivation {
     + ''
       export named_cc=${targetPrefix}cc
       export named_cxx=${targetPrefix}c++
+      export needsTarget=0
 
       if [ -e $ccPath/${targetPrefix}gcc ]; then
         wrap ${targetPrefix}gcc $wrapper $ccPath/${targetPrefix}gcc
@@ -215,6 +216,8 @@ stdenv.mkDerivation {
         export named_cc=${targetPrefix}gcc
         export named_cxx=${targetPrefix}g++
       elif [ -e $ccPath/clang ]; then
+        needsTarget=1
+        export defaultTarget=${targetPlatform.config}
         wrap ${targetPrefix}clang $wrapper $ccPath/clang
         ln -s ${targetPrefix}clang $out/bin/${targetPrefix}cc
         export named_cc=${targetPrefix}clang
@@ -225,6 +228,8 @@ stdenv.mkDerivation {
         wrap ${targetPrefix}g++ $wrapper $ccPath/${targetPrefix}g++
         ln -s ${targetPrefix}g++ $out/bin/${targetPrefix}c++
       elif [ -e $ccPath/clang++ ]; then
+        needsTarget=1
+        export defaultTarget=${targetPlatform.config}
         wrap ${targetPrefix}clang++ $wrapper $ccPath/clang++
         ln -s ${targetPrefix}clang++ $out/bin/${targetPrefix}c++
       fi
@@ -297,14 +302,6 @@ stdenv.mkDerivation {
       fi
     ''
 
-    ##
-    ## General Clang support
-    ##
-    + optionalString isClang ''
-
-      echo "-target ${targetPlatform.config}" >> $out/nix-support/cc-cflags
-    ''
-
     ##
     ## GCC libs for non-GCC support
     ##