Enable the -Wundef warning for clang

webrtc/modules/desktop_capture/differ_block_unittest.cc

 /*
  *  Copyright (c) 2013 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 "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 #include "webrtc/modules/desktop_capture/differ_block.h"
 
 namespace webrtc {
 
 // Run 900 times to mimic 1280x720.
 // TODO(fbarchard): Remove benchmark once performance is non-issue.
 static const int kTimesToRun = 900;
 
 static void GenerateData(uint8_t* data, int size) {
   for (int i = 0; i < size; ++i) {
@@ skipping 55 matching lines @@
   PrepareBuffers(block1, block2);
   block2[0] += 1;
 
   for (int i = 0; i < kTimesToRun; ++i) {
     int result = BlockDifference(block1, block2, kBlockSize * kBytesPerPixel);
     EXPECT_EQ(1, result);
   }
 }
 
 }  // namespace webrtc