Enable the -Wundef warning for clang

webrtc/modules/audio_processing/vad/pole_zero_filter_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 "webrtc/modules/audio_processing/vad/pole_zero_filter.h"
 
 #include <math.h>
 #include <stdio.h>
 
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_processing/vad/vad_audio_proc_internal.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 static const int kInputSamples = 50;
 
 static const int16_t kInput[kInputSamples] = {
     -2136,  -7116, 10715,  2464,   3164,   8139,   11393, 24013, -32117, -5544,
     -27740, 10181, 14190,  -24055, -15912, 17393,  6359,  -9950, -13894, 32432,
@@ skipping 65 matching lines @@
 
 TEST_F(PoleZeroFilterTest, TwentyFiveSubframes) {
   FilterSubframes(25);
 }
 
 TEST_F(PoleZeroFilterTest, FiftySubframes) {
   FilterSubframes(50);
 }
 
 }  // namespace webrtc