Enable the -Wundef warning for clang

webrtc/video/report_block_stats_unittest.cc

 /*
  *  Copyright (c) 2014 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 "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/video/report_block_stats.h"
 
 namespace webrtc {
 
 class ReportBlockStatsTest : public ::testing::Test {
  protected:
   ReportBlockStatsTest() : kSsrc1(0x12345), kSsrc2(0x23456) {}
 
   void SetUp() override {
@@ skipping 115 matching lines @@
   // fl: 100 * (15-10) / (24100-24000) = 5%
   stats.Store(RtcpReportBlockToRtcpStatistics(block1_2_), kRemoteSsrc, kSsrc1);
   EXPECT_EQ(5, stats.FractionLostInPercent());
   // fl: 100 * (50-10) / (24200-24000) = 20%
   stats.Store(RtcpReportBlockToRtcpStatistics(block1_3_), kRemoteSsrc, kSsrc1);
   EXPECT_EQ(20, stats.FractionLostInPercent());
 }
 
 }  // namespace webrtc