Enable the -Wundef warning for clang

webrtc/modules/remote_bitrate_estimator/test/packet_receiver.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 "webrtc/modules/remote_bitrate_estimator/test/packet_receiver.h"
 
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/common.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/bwe.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_framework.h"
 #include "webrtc/modules/rtp_rtcp/include/receive_statistics.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 namespace testing {
 namespace bwe {
@@ skipping 112 matching lines @@
 float PacketReceiver::GlobalPacketLoss() {
   return bwe_receiver_->GlobalReceiverPacketLossRatio();
 }
 
 Stats<double> PacketReceiver::GetDelayStats() const {
   return delay_stats_;
 }
 }  // namespace bwe
 }  // namespace testing
 }  // namespace webrtc