Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/neteq_external_decoder_unittest.cc

 /*
  *  Copyright (c) 2013 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.
  */
 
 // Test to verify correct operation for externally created decoders.
 
 #include <memory>
 
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/modules/audio_coding/codecs/builtin_audio_decoder_factory.h"
 #include "webrtc/modules/audio_coding/neteq/mock/mock_external_decoder_pcm16b.h"
 #include "webrtc/modules/audio_coding/neteq/tools/input_audio_file.h"
 #include "webrtc/modules/audio_coding/neteq/tools/neteq_external_decoder_test.h"
 #include "webrtc/modules/audio_coding/neteq/tools/rtp_generator.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
@@ skipping 420 matching lines @@
                                                         kStartSeqeunceNumber,
                                                         kStartTimestamp,
                                                         kJumpFromTimestamp,
                                                         kJumpToTimestamp));
 
   RunTest(130);  // Run 130 laps @ 10 ms each in the test loop.
   EXPECT_EQ(kRecovered, test_state_);
 }
 
 }  // namespace webrtc