Enable the -Wundef warning for clang

webrtc/common_audio/vad/vad_unittest.h

 /*
  *  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.
  */
 
 #ifndef WEBRTC_COMMON_AUDIO_VAD_VAD_UNITTEST_H
 #define WEBRTC_COMMON_AUDIO_VAD_VAD_UNITTEST_H
 
 #include <stddef.h>  // size_t
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/typedefs.h"
 
 namespace {
 
 // Modes we support
 const int kModes[] = { 0, 1, 2, 3 };
 const size_t kModesSize = sizeof(kModes) / sizeof(*kModes);
 
 // Rates we support.
@@ skipping 12 matching lines @@
  protected:
   VadTest();
   virtual void SetUp();
   virtual void TearDown();
 
   // Returns true if the rate and frame length combination is valid.
   bool ValidRatesAndFrameLengths(int rate, size_t frame_length);
 };
 
 #endif  // WEBRTC_COMMON_AUDIO_VAD_VAD_UNITTEST_H