Enable the -Wundef warning for clang

webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports_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 "webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.h"
 
-#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/base/random.h"
 #include "webrtc/test/rtcp_packet_parser.h"
 
 using testing::ElementsAre;
 using testing::ElementsAreArray;
 using testing::IsEmpty;
 using testing::make_tuple;
 using webrtc::rtcp::Dlrr;
 using webrtc::rtcp::ExtendedReports;
 using webrtc::rtcp::ReceiveTimeInfo;
@@ skipping 304 matching lines @@
   for (size_t i = 0; i < kMaxBlocks; ++i)
     EXPECT_TRUE(xr.AddDlrr(dlrr));
   EXPECT_FALSE(xr.AddDlrr(dlrr));
 
   VoipMetric voip_metric = Rand<VoipMetric>();
   for (size_t i = 0; i < kMaxBlocks; ++i)
     EXPECT_TRUE(xr.AddVoipMetric(voip_metric));
   EXPECT_FALSE(xr.AddVoipMetric(voip_metric));
 }
 }  // namespace webrtc