tests.cc-wrapper: do not test sanitizers on darwin

They are not supported yet.

https://github.com/NixOS/nixpkgs/pull/41284#issuecomment-394977350

pkgs/test/cc-wrapper/default.nix

@@ -1,8 +1,9 @@
 { stdenv }:
 with stdenv.lib;
 let
+  # Sanitizers are not supported on Darwin.
   # Sanitizer headers aren't available in older libc++ stdenvs due to a bug
-  sanitizersBroken = stdenv.cc.isClang && builtins.compareVersions (getVersion stdenv.cc.name) "6.0.0" < 0;
+  sanitizersBroken = stdenv.isDarwin || stdenv.cc.isClang && builtins.compareVersions (getVersion stdenv.cc.name) "6.0.0" < 0;
 in stdenv.mkDerivation {
   name = "cc-wrapper-test";