Enable the -Wundef warning for clang

webrtc/modules/audio_processing/vad/pitch_internal_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/pitch_internal.h"
 
 #include <math.h>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 TEST(PitchInternalTest, test) {
   const int kSamplingRateHz = 8000;
   const int kNumInputParameters = 4;
   const int kNumOutputParameters = 3;
   // Inputs
   double log_old_gain = log(0.5);
   double gains[] = {0.6, 0.2, 0.5, 0.4};
 
   double old_lag = 70;
@@ skipping 15 matching lines @@
                               kNumOutputParameters, &log_old_gain, &old_lag,
                               log_pitch_gain, pitch_lag_hz);
 
   for (int n = 0; n < 3; n++) {
     EXPECT_NEAR(pitch_lag_hz[n], expected_pitch_lag_hz[n], 1e-6);
     EXPECT_NEAR(log_pitch_gain[n], expected_log_pitch_gain[n], 1e-8);
   }
   EXPECT_NEAR(old_lag, expected_old_lag, 1e-6);
   EXPECT_NEAR(log_old_gain, expected_log_old_gain, 1e-8);
 }