Enable the -Wundef warning for clang

webrtc/modules/video_coding/codecs/vp8/default_temporal_layers_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 "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/video_coding/include/video_codec_interface.h"
 #include "webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.h"
 
 #include "vpx/vpx_encoder.h"
 #include "vpx/vp8cx.h"
 
 namespace webrtc {
 
 enum {
   kTemporalUpdateLast = VP8_EFLAG_NO_UPD_GF | VP8_EFLAG_NO_UPD_ARF |
@@ skipping 175 matching lines @@
     EXPECT_EQ(expected_temporal_idx[i], vp8_info.temporalIdx);
     EXPECT_EQ(true, vp8_info.layerSync);
     timestamp += 3000;
   }
   EXPECT_EQ(expected_flags[7], tl.EncodeFlags(timestamp));
   tl.PopulateCodecSpecific(false, &vp8_info, 0);
   EXPECT_EQ(expected_temporal_idx[7], vp8_info.temporalIdx);
   EXPECT_EQ(true, vp8_info.layerSync);
 }
 }  // namespace webrtc