pass clangcl compile options to ignore warnings in gflags.cc

third_party/gflags/gflags.gyp

 #
 # Copyright 2014 The LibYuv Project Authors. All rights reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS. All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # This is a copy of WebRTC's gflags.gyp.
@@ skipping 45 matching lines @@
       'conditions': [
         ['OS=="win"', {
           'sources': [
             'src/windows/port.cc',
           ],
           # Suppress warnings about WIN32_LEAN_AND_MEAN and size_t truncation.
           'msvs_disabled_warnings': [4005, 4267],
         }],
         # TODO(andrew): Look into fixing this warning upstream:
         # http://code.google.com/p/webrtc/issues/detail?id=760
+        ['OS=="win" and clang==1', {
+          'msvs_settings': {
+            'VCCLCompilerTool': {
+              'AdditionalOptions!': [
+                '-Wheader-hygiene',  # Suppress warning about using namespace.
+              ],
+              'AdditionalOptions': [
+                '-Wno-unused-local-typedef',  # Suppress unused private typedef.
+              ],
+            },
+          },
+        }],
         ['clang==1', {
           'cflags!': ['-Wheader-hygiene',],
           'xcode_settings': {
             'WARNING_CFLAGS!': ['-Wheader-hygiene',],
           },
         }],
       ],
     },
   ],
 }