Enable the -Wundef warning for clang

webrtc/modules/pacing/mock/mock_paced_sender.h

 /*
  *  Copyright (c) 2013 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_PACING_MOCK_MOCK_PACED_SENDER_H_
 #define WEBRTC_MODULES_PACING_MOCK_MOCK_PACED_SENDER_H_
 
 #include <vector>
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 
 #include "webrtc/modules/pacing/paced_sender.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 class MockPacedSender : public PacedSender {
  public:
   MockPacedSender() : PacedSender(Clock::GetRealTimeClock(), nullptr) {}
   MOCK_METHOD6(SendPacket, bool(Priority priority,
                                 uint32_t ssrc,
                                 uint16_t sequence_number,
                                 int64_t capture_time_ms,
                                 size_t bytes,
                                 bool retransmission));
   MOCK_METHOD2(CreateProbeCluster, void(int, int));
   MOCK_METHOD1(SetEstimatedBitrate, void(uint32_t));
   MOCK_CONST_METHOD0(QueueInMs, int64_t());
   MOCK_CONST_METHOD0(QueueInPackets, int());
   MOCK_CONST_METHOD0(ExpectedQueueTimeMs, int64_t());
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_PACING_MOCK_MOCK_PACED_SENDER_H_