Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/cng/audio_encoder_cng_unittest.cc

 /*
  *  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.
  */
 
 #include <memory>
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/base/gtest.h"

[kjellander_webrtc, 2016/09/23 12:32:38]

sort

 #include "webrtc/base/constructormagic.h"
 #include "webrtc/common_audio/vad/mock/mock_vad.h"
 #include "webrtc/modules/audio_coding/codecs/cng/audio_encoder_cng.h"
 #include "webrtc/modules/audio_coding/codecs/mock/mock_audio_encoder.h"
 
 using ::testing::Return;
 using ::testing::_;
 using ::testing::SetArgPointee;
 using ::testing::InSequence;
 using ::testing::Invoke;
@@ skipping 471 matching lines @@
       .WillRepeatedly(Return(7U));
   for (int i = 0; i < 6; ++i)
     Encode();
   EXPECT_DEATH(Encode(),
                "Frame size cannot be larger than 60 ms when using VAD/CNG.");
 }
 
 #endif  // GTEST_HAS_DEATH_TEST
 
 }  // namespace webrtc