Enable the -Wundef warning for clang

webrtc/modules/desktop_capture/screen_capturer_mac_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 "webrtc/modules/desktop_capture/screen_capturer.h"
 
 #include <ApplicationServices/ApplicationServices.h>
 
 #include <memory>
 #include <ostream>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/desktop_capture/desktop_capture_options.h"
 #include "webrtc/modules/desktop_capture/desktop_frame.h"
 #include "webrtc/modules/desktop_capture/desktop_geometry.h"
 #include "webrtc/modules/desktop_capture/desktop_region.h"
 #include "webrtc/modules/desktop_capture/mac/desktop_configuration.h"
 #include "webrtc/modules/desktop_capture/screen_capturer_mock_objects.h"
 
 using ::testing::_;
 using ::testing::AnyNumber;
 using ::testing::Return;
@@ skipping 64 matching lines @@
   capturer_->Start(&callback_);
 
   // Check that we get an initial full-screen updated.
   capturer_->Capture(DesktopRegion());
 
   // Check that subsequent dirty rects are propagated correctly.
   capturer_->Capture(DesktopRegion());
 }
 
 }  // namespace webrtc