gcc-wrapper: parameterize setup-hook

The default setup-hook for gcc-wrapper adds include directories with
-isystem, which upsets the order -I flags are processed. This adds an
alternative setup-hook that only uses -I flags. The build system's
ordering of -I flags is then respected. This is important when different
packages provide includes with the same name, such as building packages
that depend on Qt4 and Qt5.

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

@@ -8,6 +8,7 @@
 { name ? "", stdenv, nativeTools, nativeLibc, nativePrefix ? ""
 , gcc ? null, libc ? null, binutils ? null, coreutils ? null, shell ? stdenv.shell
 , zlib ? null, extraPackages ? []
+, setupHook ? ./setup-hook.sh
 }:
 
 with stdenv.lib;
@@ -199,7 +200,7 @@ stdenv.mkDerivation {
     ''
 
     + ''
-      substituteAll ${./setup-hook.sh} $out/nix-support/setup-hook
+      substituteAll ${setupHook} $out/nix-support/setup-hook
       substituteAll ${./add-flags} $out/nix-support/add-flags.sh
       cp -p ${./utils.sh} $out/nix-support/utils.sh
 

pkgs/build-support/gcc-wrapper/setup-hook-stdinc.sh

@@ -0,0 +1,38 @@
+export NIX_CC=@out@
+
+addCVars () {
+    if [ -d $1/include ]; then
+        export NIX_CFLAGS_COMPILE+=" -I $1/include"
+    fi
+
+    if [ -d $1/lib64 -a ! -L $1/lib64 ]; then
+        export NIX_LDFLAGS+=" -L$1/lib64"
+    fi
+
+    if [ -d $1/lib ]; then
+        export NIX_LDFLAGS+=" -L$1/lib"
+    fi
+}
+
+envHooks+=(addCVars)
+
+# Note: these come *after* $out in the PATH (see setup.sh).
+
+if [ -n "@gcc@" ]; then
+    addToSearchPath PATH @gcc@/bin
+fi
+
+if [ -n "@binutils@" ]; then
+    addToSearchPath PATH @binutils@/bin
+fi
+
+if [ -n "@libc@" ]; then
+    addToSearchPath PATH @libc@/bin
+fi
+
+if [ -n "@coreutils@" ]; then
+    addToSearchPath PATH @coreutils@/bin
+fi
+
+export CC=gcc
+export CXX=g++