Enable the -Wundef warning for clang

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

 /*
  *  Copyright (c) 2014 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_ENCODER_H_
 #define WEBRTC_MODULES_AUDIO_CODING_CODECS_MOCK_MOCK_AUDIO_ENCODER_H_
 
 #include <string>
 
 #include "webrtc/base/array_view.h"
 #include "webrtc/modules/audio_coding/codecs/audio_encoder.h"
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 
 namespace webrtc {
 
 class MockAudioEncoder : public AudioEncoder {
  public:
   // TODO(nisse): Valid overrides commented out, because the gmock
   // methods don't use any override declarations, and we want to avoid
   // warnings from -Winconsistent-missing-override. See
   // http://crbug.com/428099.
   ~MockAudioEncoder() /* override */ { Die(); }
@@ skipping 60 matching lines @@
 
    private:
     AudioEncoder::EncodedInfo info_;
     rtc::ArrayView<const uint8_t> payload_;
   };
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_MOCK_MOCK_AUDIO_ENCODER_H_