Enable the -Wundef warning for clang

webrtc/modules/rtp_rtcp/test/testFec/test_fec.cc

 /*
  *  Copyright (c) 2012 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.
  */
 
 /*
  * Test application for core FEC algorithm. Calls encoding and decoding
  * functions in ForwardErrorCorrection directly.
  */
 
 #include <string.h>
 #include <time.h>
 
 #include <list>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/random.h"
 #include "webrtc/modules/rtp_rtcp/source/byte_io.h"
 #include "webrtc/modules/rtp_rtcp/source/forward_error_correction.h"
 #include "webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 // #define VERBOSE_OUTPUT
 
 namespace webrtc {
 namespace fec_private_tables {
@@ skipping 416 matching lines @@
   }    // loop over mask types
 
   // Have DecodeFec clear the recovered packet list.
   fec->ResetState(&recovered_packet_list);
   ASSERT_TRUE(recovered_packet_list.empty())
       << "Recovered packet list is not empty";
 }
 
 }  // namespace test
 }  // namespace webrtc