Enable the -Wundef warning for clang

webrtc/modules/audio_processing/vad/vad_audio_proc_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.
  */
 
 // We don't test the value of pitch gain and lags as they are created by iSAC
 // routines. However, interpolation of pitch-gain and lags is in a separate
 // class and has its own unit-test.
 
 #include "webrtc/modules/audio_processing/vad/vad_audio_proc.h"
 
 #include <math.h>
 #include <stdio.h>
 
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/vad/common.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 TEST(AudioProcessingTest, DISABLED_ComputingFirstSpectralPeak) {
   VadAudioProc audioproc;
 
   std::string peak_file_name =
@@ skipping 21 matching lines @@
       for (size_t n = 0; n < features.num_frames; n++)
         EXPECT_NEAR(features.spectral_peak[n], sp[n], 3);
     }
   }
 
   fclose(peak_file);
   fclose(pcm_file);
 }
 
 }  // namespace webrtc