Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/sync_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_coding/neteq/sync_buffer.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 TEST(SyncBuffer, CreateAndDestroy) {
   // Create a SyncBuffer with two channels and 10 samples each.
   static const size_t kLen = 10;
   static const size_t kChannels = 2;
   SyncBuffer sync_buffer(kChannels, kLen);
   EXPECT_EQ(kChannels, sync_buffer.Channels());
   EXPECT_EQ(kLen, sync_buffer.Size());
@@ skipping 140 matching lines @@
   output_ptr = output2.data_;
   for (size_t i = kNewLen / 2; i < kNewLen; ++i) {
     for (size_t channel = 0; channel < kChannels; ++channel) {
       EXPECT_EQ(new_data[channel][i], *output_ptr);
       ++output_ptr;
     }
   }
 }
 
 }  // namespace webrtc