Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/mock/mock_dtmf_buffer.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_AUDIO_CODING_NETEQ_MOCK_MOCK_DTMF_BUFFER_H_
 #define WEBRTC_MODULES_AUDIO_CODING_NETEQ_MOCK_MOCK_DTMF_BUFFER_H_
 
 #include "webrtc/modules/audio_coding/neteq/dtmf_buffer.h"
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 
 namespace webrtc {
 
 class MockDtmfBuffer : public DtmfBuffer {
  public:
   MockDtmfBuffer(int fs) : DtmfBuffer(fs) {}
   virtual ~MockDtmfBuffer() { Die(); }
   MOCK_METHOD0(Die, void());
   MOCK_METHOD0(Flush,
       void());
   MOCK_METHOD1(InsertEvent,
       int(const DtmfEvent& event));
   MOCK_METHOD2(GetEvent,
       bool(uint32_t current_timestamp, DtmfEvent* event));
   MOCK_CONST_METHOD0(Length,
       size_t());
   MOCK_CONST_METHOD0(Empty,
       bool());
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_MOCK_MOCK_DTMF_BUFFER_H_