Enable the -Wundef warning for clang

webrtc/modules/audio_coding/audio_network_adaptor/mock/mock_debug_dump_writer.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_AUDIO_NETWORK_ADAPTOR_MOCK_MOCK_DEBUG_DUMP_WRITER_H_
 #define WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_MOCK_MOCK_DEBUG_DUMP_WRITER_H_
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/debug_dump_writer.h"
 
 namespace webrtc {
 
 class MockDebugDumpWriter : public DebugDumpWriter {
  public:
   virtual ~MockDebugDumpWriter() { Die(); }
   MOCK_METHOD0(Die, void());
 
   MOCK_METHOD2(DumpEncoderRuntimeConfig,
                void(const AudioNetworkAdaptor::EncoderRuntimeConfig& config,
                     int64_t timestamp));
   MOCK_METHOD2(DumpNetworkMetrics,
                void(const Controller::NetworkMetrics& metrics,
                     int64_t timestamp));
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_AUDIO_NETWORK_ADAPTOR_MOCK_MOCK_DEBUG_DUMP_WRITER_H_