Remove gccStdInc

This reverts d927da8dae. Having a copy
of gcc-wrapper/setup-hook.sh is bad for maintainability - it had
already started to diverge. Also, gccStdInc gave a nix-env conflict
with the standard gcc. And it wasn't actually used in Nixpkgs.

Instead, if you really need to change "-isystem" to "-I", you can now
set ccIncludeFlag to "-I".

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

@@ -9,7 +9,6 @@
 , cc ? null, libc ? null, binutils ? null, coreutils ? null, shell ? stdenv.shell
 , zlib ? null, extraPackages ? []
 , dyld ? null # TODO: should this be a setup-hook on dyld?
-, setupHook ? ./setup-hook.sh
 }:
 
 with stdenv.lib;
@@ -226,7 +225,7 @@ stdenv.mkDerivation {
     ''
 
     + ''
-      substituteAll ${setupHook} $out/nix-support/setup-hook.tmp
+      substituteAll ${./setup-hook.sh} $out/nix-support/setup-hook.tmp
       cat $out/nix-support/setup-hook.tmp >> $out/nix-support/setup-hook
       rm $out/nix-support/setup-hook.tmp