Enable the -Wundef warning for clang

webrtc/modules/video_coding/video_sender_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.
  */
 
 #include <memory>
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/video_coding/include/mock/mock_video_codec_interface.h"
 #include "webrtc/modules/video_coding/codecs/vp8/include/vp8.h"
 #include "webrtc/modules/video_coding/codecs/vp8/include/vp8_common_types.h"
 #include "webrtc/modules/video_coding/codecs/vp8/temporal_layers.h"
 #include "webrtc/modules/video_coding/include/mock/mock_vcm_callbacks.h"
 #include "webrtc/modules/video_coding/include/video_coding.h"
 #include "webrtc/modules/video_coding/video_coding_impl.h"
 #include "webrtc/modules/video_coding/test/test_util.h"
 #include "webrtc/system_wrappers/include/clock.h"
 #include "webrtc/test/frame_generator.h"
@@ skipping 481 matching lines @@
   }
   {
     // TODO(andresp): Find out why this fails with framerate = 7.5
     Vp8StreamInfo expected = {{7.0, 7.0, 7.0}, {high_b, high_b, high_b}};
     EXPECT_THAT(SimulateWithFramerate(7.0), MatchesVp8StreamInfo(expected));
   }
 }
 }  // namespace
 }  // namespace vcm
 }  // namespace webrtc