Don't link with audio codecs that we don't use

webrtc/modules/audio_coding/main/acm2/codec_owner.cc

 /*
  *  Copyright (c) 2015 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 113 matching lines @@
     return rtc_make_scoped_ptr(new AudioEncoderG722(speech_inst));
   } else {
     FATAL() << "Could not create encoder of type " << speech_inst.plname;
     return rtc::scoped_ptr<AudioEncoder>();
   }
 }
 
 AudioEncoder* CreateRedEncoder(int red_payload_type,
                                AudioEncoder* encoder,
                                rtc::scoped_ptr<AudioEncoder>* red_encoder) {
-  if (red_payload_type == -1) {
-    red_encoder->reset();
-    return encoder;
+#ifdef WEBRTC_CODEC_RED
+  if (red_payload_type != -1) {
+    AudioEncoderCopyRed::Config config;
+    config.payload_type = red_payload_type;
+    config.speech_encoder = encoder;
+    red_encoder->reset(new AudioEncoderCopyRed(config));
+    return red_encoder->get();
   }
-  AudioEncoderCopyRed::Config config;
-  config.payload_type = red_payload_type;
-  config.speech_encoder = encoder;
-  red_encoder->reset(new AudioEncoderCopyRed(config));
-  return red_encoder->get();
+#endif
+
+  red_encoder->reset();
+  return encoder;
 }
 
 void CreateCngEncoder(int cng_payload_type,
                       ACMVADMode vad_mode,
                       AudioEncoder* encoder,
                       rtc::scoped_ptr<AudioEncoder>* cng_encoder) {
   if (cng_payload_type == -1) {
     cng_encoder->reset();
     return;
   }
@@ skipping 79 matching lines @@
 }
 
 const AudioEncoder* CodecOwner::SpeechEncoder() const {
   RTC_DCHECK(!speech_encoder_ || !external_speech_encoder_);
   return external_speech_encoder_ ? external_speech_encoder_
                                   : speech_encoder_.get();
 }
 
 }  // namespace acm2
 }  // namespace webrtc