Enable the -Wundef warning for clang

webrtc/modules/congestion_controller/delay_based_bwe_unittest_helper.h

 /*
  *  Copyright (c) 2016 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.
  */
 
 #ifndef WEBRTC_MODULES_CONGESTION_CONTROLLER_DELAY_BASED_BWE_UNITTEST_HELPER_H_
 #define WEBRTC_MODULES_CONGESTION_CONTROLLER_DELAY_BASED_BWE_UNITTEST_HELPER_H_
 
 #include <list>
 #include <map>
 #include <memory>
 #include <utility>
 #include <vector>
 
-#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/system_wrappers/include/clock.h"
 
 namespace webrtc {
 namespace test {
 
 class TestBitrateObserver : public RemoteBitrateObserver {
  public:
   TestBitrateObserver() : updated_(false), latest_bitrate_(0) {}
@@ skipping 132 matching lines @@
   std::unique_ptr<test::TestBitrateObserver> bitrate_observer_;
   std::unique_ptr<RemoteBitrateEstimator> bitrate_estimator_;
   std::unique_ptr<test::StreamGenerator> stream_generator_;
   int64_t arrival_time_offset_ms_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(DelayBasedBweTest);
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_DELAY_BASED_BWE_UNITTEST_HELPER_H_