Enable the -Wundef warning for clang

webrtc/test/mock_voice_engine.h

 /*
  *  Copyright (c) 2015 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_AUDIO_MOCK_VOICE_ENGINE_H_
 #define WEBRTC_AUDIO_MOCK_VOICE_ENGINE_H_
 
 #include <memory>
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/test/mock_voe_channel_proxy.h"
 #include "webrtc/voice_engine/voice_engine_impl.h"
 
 namespace webrtc {
 namespace test {
 
 // NOTE: This class inherits from VoiceEngineImpl so that its clients will be
 // able to get the various interfaces as usual, via T::GetInterface().
 class MockVoiceEngine : public VoiceEngineImpl {
  public:
@@ skipping 301 matching lines @@
   // functor implementing the default version of ChannelProxyFactory, above.
   // GMock creates an unfortunate copy of the functor, which would cause us to
   // return a dangling reference. Fortunately, this should go away once
   // voe::Channel does.
   rtc::scoped_refptr<AudioDecoderFactory> decoder_factory_;
 };
 }  // namespace test
 }  // namespace webrtc
 
 #endif  // WEBRTC_AUDIO_MOCK_VOICE_ENGINE_H_