Moved the aec_rdft*.c files to be built using C++

webrtc/modules/audio_processing/aec/aec_rdft_neon.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.
  */
 
@@ skipping 335 matching lines @@
   a[65] = -a[65];
 }
 
 void aec_rdft_init_neon(void) {
   cft1st_128 = cft1st_128_neon;
   cftmdl_128 = cftmdl_128_neon;
   rftfsub_128 = rftfsub_128_neon;
   rftbsub_128 = rftbsub_128_neon;
 }