Enable the -Wundef warning for clang

webrtc/modules/remote_bitrate_estimator/inter_arrival_unittest.cc

 /*
  *  Copyright (c) 2013 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/common_types.h"
 #include "webrtc/modules/remote_bitrate_estimator/inter_arrival.h"
 
 namespace webrtc {
 namespace testing {
 
 enum {
   kTimestampGroupLengthUs = 5000,
   kMinStep = 20,
@@ skipping 504 matching lines @@
   system_time_ms += kTimeDeltaMs;
   EXPECT_TRUE(inter_arrival_->ComputeDeltas(
       send_time_ms, arrival_time_ms, system_time_ms, kPacketSize, &send_delta,
       &arrival_delta, &size_delta));
   EXPECT_EQ(kTimeDeltaMs, static_cast<int>(send_delta));
   EXPECT_EQ(kTimeDeltaMs, arrival_delta);
   EXPECT_EQ(size_delta, 0);
 }
 }  // namespace testing
 }  // namespace webrtc