Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/isac/fix/source/transform_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/modules/audio_coding/codecs/isac/fix/source/codec.h"
 #include "webrtc/system_wrappers/include/cpu_features_wrapper.h"
 
 static const int kSamples = FRAMESAMPLES/2;
 static const int32_t spec2time_out_expected_1[kSamples] = {
   -3366470, -2285227,
   -3415765, -2310215, -3118030, -2222470, -3030254, -2192091, -3423170,
   -2216041, -3305541, -2171936, -3195767, -2095779, -3153304, -2157560,
   -3071167, -2032108, -3101190, -1972016, -3103824, -2089118, -3139811,
   -1898337, -3102801, -2055082, -3029665, -1854140, -2962586, -1966454,
@@ skipping 162 matching lines @@
   Time2SpecTester(WebRtcIsacfix_Time2SpecNeon);
 #endif
 }
 
 TEST_F(TransformTest, Spec2TimeTest) {
   Spec2TimeTester(WebRtcIsacfix_Spec2TimeC);
 #if defined(WEBRTC_HAS_NEON)
   Spec2TimeTester(WebRtcIsacfix_Spec2TimeNeon);
 #endif
 }