Enable the -Wundef warning for clang

webrtc/modules/audio_processing/voice_detection_unittest.cc

 /*
  *  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.
  */
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/array_view.h"
 #include "webrtc/modules/audio_processing/audio_buffer.h"
 #include "webrtc/modules/audio_processing/voice_detection_impl.h"
 #include "webrtc/modules/audio_processing/test/audio_buffer_tools.h"
 #include "webrtc/modules/audio_processing/test/bitexactness_tools.h"
 
 namespace webrtc {
 namespace {
 
 const int kNumFramesToProcess = 1000;
@@ skipping 91 matching lines @@
   RunBitexactnessTest(32000, 2, kFrameSizeMsReference, kStreamHasVoiceReference,
                       kLikelihoodReference);
 }
 
 TEST(VoiceDetectionBitExactnessTest, Stereo48kHz) {
   RunBitexactnessTest(48000, 2, kFrameSizeMsReference, kStreamHasVoiceReference,
                       kLikelihoodReference);
 }
 
 }  // namespace webrtc