Enable the -Wundef warning for clang

webrtc/modules/video_coding/video_coding_robustness_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 <memory>
 
-#include "testing/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gmock.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/video_coding/include/mock/mock_video_codec_interface.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/test/test_util.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 using ::testing::Return;
 using ::testing::_;
@@ skipping 194 matching lines @@
 
   clock_->AdvanceTimeMilliseconds(23);
   InsertPacket(3000, 4, false, false, kVideoFrameDelta);
 
   InsertPacket(9000, 9, true, false, kVideoFrameDelta);
   InsertPacket(9000, 10, false, false, kVideoFrameDelta);
   InsertPacket(9000, 11, false, true, kVideoFrameDelta);
   EXPECT_EQ(VCM_OK, vcm_->Decode(33));  // Decode timestamp 9000 complete.
 }
 }  // namespace webrtc