Enable the -Wundef warning for clang

webrtc/modules/rtp_rtcp/source/rtcp_packet/voip_metric_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 "webrtc/modules/rtp_rtcp/source/rtcp_packet/voip_metric.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 namespace rtcp {
 namespace {
 
 const uint32_t kRemoteSsrc = 0x23456789;
 const uint8_t kBlock[] = {0x07, 0x00, 0x00, 0x08, 0x23, 0x45, 0x67, 0x89,
                           0x01, 0x02, 0x03, 0x04, 0x11, 0x12, 0x22, 0x23,
                           0x33, 0x34, 0x44, 0x45, 0x05, 0x06, 0x07, 0x08,
                           0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x00, 0x55, 0x56,
@@ skipping 60 matching lines @@
   EXPECT_EQ(12, parsed.voip_metric().MOSCQ);
   EXPECT_EQ(13, parsed.voip_metric().RXconfig);
   EXPECT_EQ(0x5556, parsed.voip_metric().JBnominal);
   EXPECT_EQ(0x6667, parsed.voip_metric().JBmax);
   EXPECT_EQ(0x7778, parsed.voip_metric().JBabsMax);
 }
 
 }  // namespace
 }  // namespace rtcp
 }  // namespace webrtc