Enable the -Wundef warning for clang

webrtc/modules/utility/include/mock/mock_process_thread.h

 /*
  *  Copyright (c) 2014 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_UTILITY_INCLUDE_MOCK_MOCK_PROCESS_THREAD_H_
 #define WEBRTC_MODULES_UTILITY_INCLUDE_MOCK_MOCK_PROCESS_THREAD_H_
 
 #include <memory>
 
 #include "webrtc/modules/utility/include/process_thread.h"
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 
 namespace webrtc {
 
 class MockProcessThread : public ProcessThread {
  public:
   // TODO(nisse): Valid overrides commented out, because the gmock
   // methods don't use any override declarations, and we want to avoid
   // warnings from -Winconsistent-missing-override. See
   // http://crbug.com/428099.
   MOCK_METHOD0(Start, void());
   MOCK_METHOD0(Stop, void());
   MOCK_METHOD1(WakeUp, void(Module* module));
   MOCK_METHOD1(PostTask, void(rtc::QueuedTask* task));
   MOCK_METHOD1(RegisterModule, void(Module* module));
   MOCK_METHOD1(DeRegisterModule, void(Module* module));
 
   // MOCK_METHOD1 gets confused with mocking this method, so we work around it
   // by overriding the method from the interface and forwarding the call to a
   // mocked, simpler method.
   void PostTask(std::unique_ptr<rtc::QueuedTask> task) /*override*/ {
     PostTask(task.get());
   }
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_UTILITY_INCLUDE_MOCK_MOCK_PROCESS_THREAD_H_