Enable the -Wundef warning for clang

webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy_unittest.cc

 /*
  *  Copyright (c) 2015 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/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gmock.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/modules/pacing/packet_router.h"
 #include "webrtc/modules/remote_bitrate_estimator/remote_estimator_proxy.h"
 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 using ::testing::_;
 using ::testing::InSequence;
 using ::testing::Invoke;
 using ::testing::Return;
@@ skipping 322 matching lines @@
                   (packet->GetBaseTimeUs() + delta_vec[0]) / 1000);
         EXPECT_EQ(kTimeoutTimeMs - kBaseTimeMs, delta_vec[1] / 1000);
         EXPECT_EQ(1, delta_vec[2] / 1000);
         return true;
       }));
 
   Process();
 }
 
 }  // namespace webrtc