Fix repeated "-Wunknown-pragmas -Wno-error=unknown-pragmas".

tools/grit/grit_rule.gni

 # Copyright 2014 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.
 
 # Instantiate grit. This will produce a script target to run grit, and a
 # static library that compiles the .cc files.
 #
 # Parameters
 #
 #   source (required)
@@ skipping 339 matching lines @@
   # change this to including absolute paths relative to the root gen directory
   # (like "mycomponent/foo.h"). This config sets up the include path.
   grit_config = target_name + "_grit_config"
   config(grit_config) {
     if (!defined(invoker.use_qualified_include) ||
         !invoker.use_qualified_include) {
       include_dirs = [ output_dir ]
     }
 
     if ((is_linux || is_android) && enable_resource_whitelist_generation) {
-      cflags = [
-        "-Wunknown-pragmas",
-        "-Wno-error=unknown-pragmas",
-      ]
+      configs += [ "//build/config/compiler:disable_unknown_pragma" ]
     }
     visibility = target_visibility
   }
 
   grit_custom_target = target_name + "_grit"
   action(grit_custom_target) {
     script = "//tools/grit/grit.py"
 
     inputs = [
       invoker.source,
@@ skipping 115 matching lines @@
     if (defined(invoker.configs)) {
       configs += invoker.configs
     }
 
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
     output_name = grit_output_name
   }
 }