Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/isac/fix/source/filterbanks_unittest.cc

 /*
  *  Copyright (c) 2012 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_audio/signal_processing/include/signal_processing_library.h"
 #include "webrtc/modules/audio_coding/codecs/isac/fix/source/filterbank_internal.h"
 #include "webrtc/modules/audio_coding/codecs/isac/fix/source/filterbank_tables.h"
 #include "webrtc/modules/audio_coding/codecs/isac/fix/source/settings.h"
 #include "webrtc/system_wrappers/include/cpu_features_wrapper.h"
 #include "webrtc/typedefs.h"
 
 class FilterBanksTest : public testing::Test {
  protected:
   // Pass a function pointer to the Tester function.
@@ skipping 72 matching lines @@
     in[i] = WEBRTC_SPL_WORD32_MAX / (i + 1);
   }
 
   WebRtcIsacfix_HighpassFilterFixDec32(in, kSamples,
       WebRtcIsacfix_kHPStCoeffOut1Q30, state);
 
   for (int i = 0; i < kSamples; i++) {
     EXPECT_EQ(out[i], in[i]);
   }
 }