Enable the -Wundef warning for clang

webrtc/video/call_stats_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 <memory>
 
-#include "testing/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gmock.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 #include "webrtc/system_wrappers/include/metrics_default.h"
 #include "webrtc/video/call_stats.h"
 
 using ::testing::_;
 using ::testing::AnyNumber;
 using ::testing::Return;
 
@@ skipping 188 matching lines @@
   call_stats_->Process();
   call_stats_.reset();
 
   EXPECT_EQ(1, metrics::NumSamples(
                    "WebRTC.Video.AverageRoundTripTimeInMilliseconds"));
   EXPECT_EQ(1, metrics::NumEvents(
                    "WebRTC.Video.AverageRoundTripTimeInMilliseconds", kRtt));
 }
 
 }  // namespace webrtc