Enable the -Wundef warning for clang

webrtc/call/rtc_event_log_unittest_helper.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/call/rtc_event_log_unittest_helper.h"
 
 #include <string.h>
 
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/test/test_suite.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 // Files generated at build-time by the protobuf compiler.
 #ifdef WEBRTC_ANDROID_PLATFORM_BUILD
 #include "external/webrtc/webrtc/call/rtc_event_log.pb.h"
 #else
 #include "webrtc/call/rtc_event_log.pb.h"
 #endif
@@ skipping 368 matching lines @@
 
 void RtcEventLogTestHelper::VerifyLogEndEvent(
     const ParsedRtcEventLog& parsed_log,
     size_t index) {
   const rtclog::Event& event = parsed_log.events_[index];
   ASSERT_TRUE(IsValidBasicEvent(event));
   EXPECT_EQ(rtclog::Event::LOG_END, event.type());
 }
 
 }  // namespace webrtc