Enable the -Wundef warning for clang

webrtc/modules/remote_bitrate_estimator/bwe_simulations.cc

 /*
  *  Copyright (c) 2014 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/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/modules/remote_bitrate_estimator/include/remote_bitrate_estimator.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/bwe_test.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/packet_receiver.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/packet_sender.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 
 namespace webrtc {
 namespace testing {
@@ skipping 419 matching lines @@
 
   BweTest gcc_test(false);
   gcc_test.RunChoke(kFullSendSideEstimator, capacities_kbps);
 }
 
 #endif  // BWE_TEST_LOGGING_COMPILE_TIME_ENABLE
 }  // namespace bwe
 }  // namespace testing
 }  // namespace webrtc