Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/mock/mock_audio_decoder_factory.h

 /*
  *  Copyright (c) 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_MODULES_AUDIO_CODING_CODECS_MOCK_MOCK_AUDIO_DECODER_FACTORY_H_
 #define WEBRTC_MODULES_AUDIO_CODING_CODECS_MOCK_MOCK_AUDIO_DECODER_FACTORY_H_
 
 #include <vector>
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/modules/audio_coding/codecs/audio_decoder_factory.h"
 
 namespace webrtc {
 
 class MockAudioDecoderFactory : public AudioDecoderFactory {
  public:
   MOCK_METHOD0(GetSupportedDecoders, std::vector<AudioCodecSpec>());
   std::unique_ptr<AudioDecoder> MakeAudioDecoder(
       const SdpAudioFormat& format) {
@@ skipping 41 matching lines @@
     ON_CALL(*factory.get(), MakeAudioDecoderMock(_, _))
         .WillByDefault(SetArgPointee<1>(nullptr));
     EXPECT_CALL(*factory.get(), MakeAudioDecoderMock(_, _)).Times(AnyNumber());
     return factory;
   }
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_MOCK_MOCK_AUDIO_DECODER_FACTORY_H_