Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/expand_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.
  */
 
 // Unit tests for Expand class.
 
 #include "webrtc/modules/audio_coding/neteq/expand.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/safe_conversions.h"
 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
 #include "webrtc/modules/audio_coding/neteq/background_noise.h"
 #include "webrtc/modules/audio_coding/neteq/random_vector.h"
 #include "webrtc/modules/audio_coding/neteq/statistics_calculator.h"
 #include "webrtc/modules/audio_coding/neteq/sync_buffer.h"
 #include "webrtc/modules/audio_coding/neteq/tools/resample_input_audio_file.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
@@ skipping 171 matching lines @@
 
   expand_.Reset();  // Must reset in order to start a new expand period.
   ExpandUntilMuted(num_channels_, &expand_);
   expand_.SetParametersForNormalAfterExpand();
   EXPECT_FALSE(expand_.Muted());  // Should be back to unmuted.
 }
 
 // TODO(hlundin): Write more tests.
 
 }  // namespace webrtc