Enable the -Wundef warning for clang

webrtc/common_video/bitrate_adjuster_unittest.cc

 /*
  *  Copyright 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/common_video/include/bitrate_adjuster.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 class BitrateAdjusterTest : public ::testing::Test {
  public:
   BitrateAdjusterTest()
       : clock_(0),
@@ skipping 138 matching lines @@
   EXPECT_EQ(initial_target_bitrate_bps, adjuster_.GetAdjustedBitrateBps());
 
   // 1.05 * 1.05 is 1.1 which is greater than tolerance for the initial target
   // bitrate. Since we didn't advance the clock the adjuster never updated.
   target_bitrate_bps = (1 + delta_pct) * target_bitrate_bps;
   adjuster_.SetTargetBitrateBps(target_bitrate_bps);
   EXPECT_EQ(target_bitrate_bps, adjuster_.GetAdjustedBitrateBps());
 }
 
 }  // namespace webrtc