Enable the -Wundef warning for clang

webrtc/modules/video_coding/include/mock/mock_video_codec_interface.h

 /*
  *  Copyright (c) 2012 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_VIDEO_CODING_INCLUDE_MOCK_MOCK_VIDEO_CODEC_INTERFACE_H_
 #define WEBRTC_MODULES_VIDEO_CODING_INCLUDE_MOCK_MOCK_VIDEO_CODEC_INTERFACE_H_
 
 #include <string>
 #include <vector>
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/modules/video_coding/include/video_codec_interface.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 class MockEncodedImageCallback : public EncodedImageCallback {
  public:
   MOCK_METHOD3(OnEncodedImage,
                Result(const EncodedImage& encodedImage,
                       const CodecSpecificInfo* codecSpecificInfo,
@@ skipping 43 matching lines @@
                        int64_t renderTimeMs));
   MOCK_METHOD1(RegisterDecodeCompleteCallback,
                int32_t(DecodedImageCallback* callback));
   MOCK_METHOD0(Release, int32_t());
   MOCK_METHOD0(Copy, VideoDecoder*());
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_INCLUDE_MOCK_MOCK_VIDEO_CODEC_INTERFACE_H_