Enable the -Wundef warning for clang

webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc

 /*
  *  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.
  */
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/modules/pacing/paced_sender.h"
 #include "webrtc/modules/congestion_controller/delay_based_bwe.h"
 #include "webrtc/modules/congestion_controller/delay_based_bwe_unittest_helper.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 namespace {
 
@@ skipping 153 matching lines @@
 }
 
 TEST_F(DelayBasedBweTest, TestLongTimeoutAndWrap) {
   // Simulate a client leaving and rejoining the call after some multiple of
   // 64 seconds later. This will cause a zero difference in abs send times due
   // to the wrap, but a big difference in arrival time, if streams aren't
   // properly timed out.
   TestWrappingHelper(10 * 64);
 }
 }  // namespace webrtc