Enable the -Wundef warning for clang

webrtc/modules/bitrate_controller/send_side_bandwidth_estimation_unittest.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 <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/send_side_bandwidth_estimation.h"
 
 namespace webrtc {
 
 void TestProbing(bool use_delay_based) {
   MockRtcEventLog event_log;
   SendSideBandwidthEstimation bwe(&event_log);
   bwe.SetMinMaxBitrate(100000, 1500000);
   bwe.SetSendBitrate(200000);
@@ skipping 86 matching lines @@
   bwe.UpdateEstimate(now_ms);
   bwe.CurrentEstimate(&bitrate_bps, &fraction_loss, &rtt_ms);
 
   EXPECT_EQ(last_bitrate_bps, bitrate_bps);
   // The old loss rate should still be applied though.
   EXPECT_EQ(kFractionLoss, fraction_loss);
   EXPECT_EQ(kRttMs, rtt_ms);
 }
 
 }  // namespace webrtc