Enable the -Wundef warning for clang

webrtc/modules/video_coding/jitter_buffer_unittest.cc

 /*
  *  Copyright (c) 2011 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 <string>
 
 #include <list>
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gtest.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/modules/video_coding/frame_buffer.h"
 #include "webrtc/modules/video_coding/jitter_buffer.h"
 #include "webrtc/modules/video_coding/media_opt_util.h"
 #include "webrtc/modules/video_coding/packet.h"
 #include "webrtc/modules/video_coding/test/stream_generator.h"
 #include "webrtc/modules/video_coding/test/test_util.h"
 #include "webrtc/system_wrappers/include/clock.h"
 #include "webrtc/system_wrappers/include/field_trial.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 #include "webrtc/system_wrappers/include/metrics_default.h"
@@ skipping 2600 matching lines @@
 
   // Stream should be decodable from this point.
   clock_->AdvanceTimeMilliseconds(kDefaultFramePeriodMs);
   InsertFrame(kVideoFrameDelta);
   EXPECT_TRUE(DecodeCompleteFrame());
   nack_list = jitter_buffer_->GetNackList(&extended);
   EXPECT_EQ(0u, nack_list.size());
 }
 
 }  // namespace webrtc