Enable the -Wundef warning for clang

webrtc/modules/video_coding/utility/h264_bitstream_parser_unittest.cc

 /*
  *  Copyright (c) 2015 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/utility/h264_bitstream_parser.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 // SPS/PPS part of below chunk.
 uint8_t kH264SpsPps[] = {0x00, 0x00, 0x00, 0x01, 0x67, 0x42, 0x80, 0x20, 0xda,
                          0x01, 0x40, 0x16, 0xe8, 0x06, 0xd0, 0xa1, 0x35, 0x00,
                          0x00, 0x00, 0x01, 0x68, 0xce, 0x06, 0xe2};
 
 // Contains enough of the image slice to contain slice QP.
 uint8_t kH264BitstreamChunk[] = {
@@ skipping 29 matching lines @@
   EXPECT_EQ(35, qp);
 
   // Parse an additional image slice.
   h264_parser.ParseBitstream(kH264BitstreamNextImageSliceChunk,
                              sizeof(kH264BitstreamNextImageSliceChunk));
   ASSERT_TRUE(h264_parser.GetLastSliceQp(&qp));
   EXPECT_EQ(37, qp);
 }
 
 }  // namespace webrtc