Enable the -Wundef warning for clang

webrtc/test/fake_audio_device.cc

 /*
  *  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.
  */
 
 #include "webrtc/test/fake_audio_device.h"
 
 #include <algorithm>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/platform_thread.h"
 #include "webrtc/modules/media_file/media_file_utility.h"
 #include "webrtc/system_wrappers/include/clock.h"
 #include "webrtc/system_wrappers/include/event_wrapper.h"
 #include "webrtc/system_wrappers/include/file_wrapper.h"
 
 namespace webrtc {
 namespace test {
 
 FakeAudioDevice::FakeAudioDevice(Clock* clock,
@@ skipping 111 matching lines @@
   rtc::CritScope cs(&lock_);
   capturing_ = true;
 }
 
 void FakeAudioDevice::Stop() {
   rtc::CritScope cs(&lock_);
   capturing_ = false;
 }
 }  // namespace test
 }  // namespace webrtc