Enable the -Wundef warning for clang

webrtc/voice_engine/voe_codec_unittest.cc

 /*
  *  Copyright (c) 2012 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 "webrtc/voice_engine/include/voe_codec.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_device/include/fake_audio_device.h"
 #include "webrtc/voice_engine/include/voe_base.h"
 #include "webrtc/voice_engine/include/voe_hardware.h"
 #include "webrtc/voice_engine/voice_engine_defines.h"
 
 namespace webrtc {
 namespace voe {
 namespace {
 
 TEST(VoECodecInst, TestCompareCodecInstances) {
@@ skipping 72 matching lines @@
   base->DeleteChannel(channel);
   base->Terminate();
   base->Release();
   voe_codec->Release();
   VoiceEngine::Delete(voe);
 }
 
 }  // namespace
 }  // namespace voe
 }  // namespace webrtc