Enable the -Wundef warning for clang

webrtc/modules/video_coding/codecs/test/packet_manipulator_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.
  */
 
 #include "webrtc/modules/video_coding/codecs/test/packet_manipulator.h"
 
 #include <queue>
 
-#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/test/predictive_packet_manipulator.h"
 #include "webrtc/test/testsupport/unittest_utils.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 namespace test {
 
 const double kNeverDropProbability = 0.0;
 const double kAlwaysDropProbability = 1.0;
@@ skipping 113 matching lines @@
 
   // Execute the test target method:
   int nbr_packets_dropped = manipulator.ManipulatePackets(&image_);
 
   // Should discard every packet after the first one.
   VerifyPacketLoss(9, nbr_packets_dropped, kPacketSizeInBytes, data, image_);
 }
 
 }  // namespace test
 }  // namespace webrtc