Enable the -Wundef warning for clang

webrtc/modules/congestion_controller/include/mock/mock_congestion_controller.h

 /*
  *  Copyright (c) 2015 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_CONGESTION_CONTROLLER_INCLUDE_MOCK_MOCK_CONGESTION_CONTROLLER_H_
 #define WEBRTC_MODULES_CONGESTION_CONTROLLER_INCLUDE_MOCK_MOCK_CONGESTION_CONTROLLER_H_
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/socket.h"
 #include "webrtc/modules/congestion_controller/include/congestion_controller.h"
 
 namespace webrtc {
 namespace test {
 
 class MockCongestionObserver : public CongestionController::Observer {
  public:
   MOCK_METHOD3(OnNetworkChanged,
@@ skipping 28 matching lines @@
                void(int bitrate_kbps,
                     int max_bitrate_kbps,
                     int min_bitrate_kbps));
   MOCK_METHOD1(OnSentPacket, void(const rtc::SentPacket& sent_packet));
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(MockCongestionController);
 };
 }  // namespace test
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_INCLUDE_MOCK_MOCK_CONGESTION_CONTROLLER_H_