Enable the -Wundef warning for clang

webrtc/common_video/libyuv/libyuv_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 <math.h>
 #include <string.h>
 
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/common_video/libyuv/include/webrtc_libyuv.h"
 #include "webrtc/test/testsupport/fileutils.h"
 #include "webrtc/video_frame.h"
 
 namespace webrtc {
 
 namespace {
 void Calc16ByteAlignedStride(int width, int* stride_y, int* stride_uv) {
   *stride_y = 16 * ((width + 15) / 16);
   *stride_uv = 16 * ((width + 31) / 32);
@@ skipping 225 matching lines @@
                              0, kVideoRotation_270,
                              rotated_res_i420_buffer.get()));
   rotated_res_i420_buffer = I420Buffer::Create(
       width_, height_, width_, (width_ + 1) / 2, (width_ + 1) / 2);
   EXPECT_EQ(0, ConvertToI420(kI420, orig_buffer_.get(), 0, 0, width_, height_,
                              0, kVideoRotation_180,
                              rotated_res_i420_buffer.get()));
 }
 
 }  // namespace webrtc