Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/red_payload_splitter_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 RedPayloadSplitter class.
 
 #include "webrtc/modules/audio_coding/neteq/red_payload_splitter.h"
 
 #include <assert.h>
 
 #include <memory>
 #include <utility>  // pair
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_coding/codecs/builtin_audio_decoder_factory.h"
 #include "webrtc/modules/audio_coding/codecs/mock/mock_audio_decoder_factory.h"
 #include "webrtc/modules/audio_coding/neteq/mock/mock_decoder_database.h"
 #include "webrtc/modules/audio_coding/neteq/packet.h"
 
 using ::testing::Return;
 using ::testing::ReturnNull;
 
 namespace webrtc {
 
@@ skipping 321 matching lines @@
   ASSERT_EQ(1u, packet_list.size());
   // Check first packet.
   packet = packet_list.front();
   VerifyPacket(packet, kPayloadLength, payload_types[0], kSequenceNumber,
                kBaseTimestamp - 2 * kTimestampOffset, 0, {0, 2});
   delete packet;
   packet_list.pop_front();
 }
 
 }  // namespace webrtc