Enable the -Wundef warning for clang

webrtc/media/base/test/mock_mediachannel.h

 /*
  *  Copyright 2016 The WebRTC 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.
  */
 
 #ifndef WEBRTC_MEDIA_BASE_TEST_MOCK_MEDIACHANNEL_H_
 #define WEBRTC_MEDIA_BASE_TEST_MOCK_MEDIACHANNEL_H_
 
 #include "webrtc/media/base/fakemediaengine.h"
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 
 namespace webrtc {
 
 class MockVideoMediaChannel : public cricket::FakeVideoMediaChannel {
  public:
   MockVideoMediaChannel() :
       cricket::FakeVideoMediaChannel(NULL, cricket::VideoOptions()) {}
   MOCK_METHOD1(GetStats, bool(cricket::VideoMediaInfo*));
 };
 
 class MockVoiceMediaChannel : public cricket::FakeVoiceMediaChannel {
  public:
   MockVoiceMediaChannel() :
       cricket::FakeVoiceMediaChannel(NULL, cricket::AudioOptions()) {}
   MOCK_METHOD1(GetStats, bool(cricket::VoiceMediaInfo*));
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MEDIA_BASE_TEST_MOCK_MEDIACHANNEL_H_