Enable the -Wundef warning for clang

webrtc/modules/audio_processing/vad/vad_circular_buffer_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/vad_circular_buffer.h"
 
 #include <stdio.h>
 
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 static const int kWidthThreshold = 7;
 static const double kValThreshold = 1.0;
 static const int kLongBuffSize = 100;
 static const int kShortBuffSize = 10;
 
 static void InsertSequentially(int k, VadCircularBuffer* circular_buffer) {
   double mean_val;
@@ skipping 97 matching lines @@
   // it shouldn't be considered transient.
   Insert(push_val, num_insertion, circular_buffer.get());
   num_non_zero_elements += num_insertion;
   EXPECT_EQ(0,
             circular_buffer->RemoveTransient(kWidthThreshold, kValThreshold));
   mean_val = circular_buffer->Mean();
   EXPECT_DOUBLE_EQ(num_non_zero_elements * push_val / kLongBuffSize, mean_val);
 }
 
 }  // namespace webrtc