Enable the -Wundef warning for clang

webrtc/modules/rtp_rtcp/test/testFec/test_packet_masks_metrics.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.
  */
 
@@ skipping 29 matching lines @@
  * The type of packet/symbol loss models considered in this test are:
  * (1) Random loss: Bernoulli process, characterized by the average loss rate.
  * (2) Bursty loss: Markov chain (Gilbert-Elliot model), characterized by two
  * parameters: average loss rate and average burst length.
 */
 
 #include <math.h>
 
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h"
 #include "webrtc/modules/rtp_rtcp/test/testFec/average_residual_loss_xor_codes.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 // Maximum number of media packets allows for XOR (RFC 5109) code.
 enum { kMaxNumberMediaPackets = 48 };
 
 // Maximum number of media packets allowed for each mask type.
@@ skipping 1011 matching lines @@
                 recovery_rate_per_loss[loss_number],
                 kRecoveryRateXorRandom[2]);
       EXPECT_GE(kMetricsXorBursty[code_index].
                 recovery_rate_per_loss[loss_number],
                 kRecoveryRateXorBursty[2]);
     }
   }
 }
 
 }  // namespace webrtc