Enable the -Wundef warning for clang

webrtc/modules/audio_processing/agc/mock_agc.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_PROCESSING_AGC_MOCK_AGC_H_
 #define WEBRTC_MODULES_AUDIO_PROCESSING_AGC_MOCK_AGC_H_
 
 #include "webrtc/modules/audio_processing/agc/agc.h"
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/modules/include/module_common_types.h"
 
 namespace webrtc {
 
 class MockAgc : public Agc {
  public:
   MOCK_METHOD2(AnalyzePreproc, float(const int16_t* audio, size_t length));
   MOCK_METHOD3(Process, int(const int16_t* audio, size_t length,
                             int sample_rate_hz));
   MOCK_METHOD1(GetRmsErrorDb, bool(int* error));
   MOCK_METHOD0(Reset, void());
   MOCK_METHOD1(set_target_level_dbfs, int(int level));
   MOCK_CONST_METHOD0(target_level_dbfs, int());
   MOCK_METHOD1(EnableStandaloneVad, void(bool enable));
   MOCK_CONST_METHOD0(standalone_vad_enabled, bool());
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_PROCESSING_AGC_MOCK_AGC_H_