Enable the -Wundef warning for clang

webrtc/modules/video_coding/protection_bitrate_calculator_unittest.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 "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/video_coding/protection_bitrate_calculator.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 static const int kCodecBitrateBps = 100000;
 
 class ProtectionBitrateCalculatorTest : public ::testing::Test {
  protected:
   enum {
@@ skipping 69 matching lines @@
 
   media_opt_.SetProtectionMethod(false /*enable_fec*/, false /* enable_nack */);
   media_opt_.SetEncodingData(640, 480, 1, 1000);
 
   uint32_t target_bitrate =
       media_opt_.SetTargetRates(kMaxBitrateBps, 30, 128, 100);
   EXPECT_EQ(kMaxBitrateBps, target_bitrate);
 }
 
 }  // namespace webrtc