pass clangcl compile options to ignore warnings in gflags.cc

third_party/gflags/gflags.gyp

 # Copyright 2011 Google Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #      http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 45 matching lines @@
         'src/gflags_completions.cc',
         'src/gflags_reporting.cc',
       ],
       'conditions': [
         ['OS=="win"', {
           'sources': [
             'src/windows/port.cc',
           ],
           # Suppress warnings about WIN32_LEAN_AND_MEAN and size_t truncation.
           'msvs_disabled_warnings': [4005, 4267],
+          'msvs_settings': {

[kjellander_webrtc, 2015/10/28 12:09:01]

After looking at the trybot failure for regular (non-Clang) build on Win it
seems you have to put this into a condition like 'OS=="win" and clang==1': 

[302/2847] LIB obj\third_party\libjpeg_turbo\libjpeg.lib
FAILED: ninja -t msvc -e environment.x64 -- E:\b\build\goma/gomacc
"E:\b\depot_tools\win_toolchain\vs2013_files\VC\bin\amd64\cl.exe" /nologo
/showIncludes /FC @obj\third_party\gflags\src\windows\gflags.port.obj.rsp /c
..\..\third_party\gflags\src\windows\port.cc
/Foobj\third_party\gflags\src\windows\gflags.port.obj
/Fdobj\third_party\gflags\gflags.cc.pdb 
cl : Command line error D8021 : invalid numeric argument
'/Wno-unused-local-typedef'

+            'VCCLCompilerTool': {
+              'AdditionalOptions!': [
+                '-Wheader-hygiene',  # Suppress warning about using namespace.
+              ],
+              'AdditionalOptions': [
+                '-Wno-unused-local-typedef',  # Suppress unused private typedef.
+              ],
+            },
+          },
         }],
         # TODO(andrew): Look into fixing this warning upstream:
         # http://code.google.com/p/webrtc/issues/detail?id=760
         ['clang==1', {
           'cflags!': ['-Wheader-hygiene',],
           'xcode_settings': {
             'WARNING_CFLAGS!': ['-Wheader-hygiene',],
           },
         }],
       ],
     },
   ],
 }