GN Mac build work

tools/gn/secondary/build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Base compiler configuration.
 config("compiler") {
   include_dirs = [ "//" ]
   if (is_win) {
     cflags = [
       "/Gy",  # Enable function-level linking.
@@ skipping 98 matching lines @@
         "-fPIC",
         "-pthread",
         "-Wl,-z,noexecstack",
         "-Wl,-z,now",
         "-Wl,-z,relro",
       ]
     }
 
     # Clang-specific compiler flags setup.
     # ------------------------------------
-    # TODO(brettw) these should be clang-only. For now, make it mac-only since
-    # that's where we always use clang.
-    if (is_mac) { # if (is_clang) {
+    if (is_clang) {
       cflags += [
         "-fcolor-diagnostics",
       ]
     }
   }
 }
 
 # runtime_library -------------------------------------------------------------
 #
 # Sets the runtime library and associated options.
@@ skipping 162 matching lines @@
     ]
 
     if (is_mac) {
       cflags += [
         "-Wnewline-eof",
       ]
     }
 
     # TODO(brettw) Ones below here should be clang-only when we have a flag
     # for it.
-    if (is_mac) { #if (is_clang) {
+    if (is_clang) {
       cflags += [
         "-Wheader-hygiene",
 
         # This warns on using ints as initializers for floats in
         # initializer lists (e.g. |int a = f(); CGSize s = { a, a };|),
         # which happens in several places in chrome code. Not sure if
         # this is worth fixing.
         "-Wno-c++11-narrowing",
 
         # Don't die on dtoa code that uses a char as an array index.
@@ skipping 74 matching lines @@
   } else {
     cflags = [ "-g1" ]
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }