Enable the -Wundef warning for clang

webrtc/modules/bitrate_controller/bitrate_controller_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 <algorithm>
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/call/mock/mock_rtc_event_log.h"
 #include "webrtc/modules/bitrate_controller/include/bitrate_controller.h"
 #include "webrtc/modules/pacing/mock/mock_paced_sender.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
 #include "webrtc/test/field_trial.h"
 
 using ::testing::Exactly;
 using ::testing::Return;
 
@@ skipping 480 matching lines @@
   clock_.AdvanceTimeMilliseconds(100);
 
   // 15 packets reported as received since last, enough to increase.
   report_blocks.push_back(CreateReportBlock(1, 2, 0, 41));
   bandwidth_observer_->OnReceivedRtcpReceiverReport(
       report_blocks, 50, clock_.TimeInMilliseconds());
   expected_bitrate_bps = expected_bitrate_bps * 1.08 + 1000;
   EXPECT_EQ(expected_bitrate_bps, bitrate_observer_.last_bitrate_);
   clock_.AdvanceTimeMilliseconds(1000);
 }