Enable the -Wundef warning for clang

webrtc/test/frame_generator_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 <stdio.h>
 
 #include <memory>
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/test/frame_generator.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 namespace test {
 
 static const int kFrameWidth = 4;
 static const int kFrameHeight = 4;
 
 class FrameGeneratorTest : public ::testing::Test {
@@ skipping 111 matching lines @@
     CheckFrameAndMutate(generator->NextFrame(), 0, 0, 0);
   for (int i = 0; i < kRepeatCount; ++i)
     CheckFrameAndMutate(generator->NextFrame(), 127, 127, 127);
   for (int i = 0; i < kRepeatCount; ++i)
     CheckFrameAndMutate(generator->NextFrame(), 255, 255, 255);
   CheckFrameAndMutate(generator->NextFrame(), 0, 0, 0);
 }
 
 }  // namespace test
 }  // namespace webrtc