Enable the -Wundef warning for clang

webrtc/tools/frame_editing/frame_editing_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 <stdio.h>
 #include <stdlib.h>
 
 #include <fstream>
 #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/tools/frame_editing/frame_editing_lib.h"
 
 namespace webrtc {
 namespace test {
 
 const int kWidth = 352;
 const int kHeight = 288;
 const size_t kFrameSize = CalcBufferSize(kI420, kWidth, kHeight);
@@ skipping 179 matching lines @@
       EXPECT_EQ(kFrameSize, num_bytes_read_);
       EXPECT_EQ(0, memcmp(original_buffer_.get(), edited_buffer_.get(),
                           kFrameSize));
     }
   }
   CompareToTheEnd(edited_fid_, original_fid_, &original_buffer_,
                   &edited_buffer_);
 }
 }  // namespace test
 }  // namespace webrtc