Add a gyp/gn variable for whether to use iLBC or not

webrtc/modules/audio_coding/audio_coding.gypi

Index: webrtc/modules/audio_coding/audio_coding.gypi
diff --git a/webrtc/modules/audio_coding/audio_coding.gypi b/webrtc/modules/audio_coding/audio_coding.gypi
index abdb1915c33ac4699b3b2a734fd2ba800f1b7f06..d64fbeee292abd00b540596cb9e84ab6d70ad548 100644
--- a/webrtc/modules/audio_coding/audio_coding.gypi
+++ b/webrtc/modules/audio_coding/audio_coding.gypi
@@ -32,6 +32,10 @@
     ],
     'audio_coding_defines': [],
     'conditions': [
+      ['include_ilbc==1', {
+        'audio_coding_dependencies': ['ilbc',],
+        'audio_coding_defines': ['WEBRTC_CODEC_ILBC',],
+      }],
       ['include_opus==1', {
         'audio_coding_dependencies': ['webrtc_opus',],
         'audio_coding_defines': ['WEBRTC_CODEC_OPUS',],
@@ -50,8 +54,8 @@
         'audio_coding_defines': ['WEBRTC_CODEC_G722',],
       }],
       ['build_with_mozilla==0 and build_with_chromium==0', {
-        'audio_coding_dependencies': ['ilbc', 'red',],
-        'audio_coding_defines': ['WEBRTC_CODEC_ILBC', 'WEBRTC_CODEC_RED',],
+        'audio_coding_dependencies': ['red',],
+        'audio_coding_defines': ['WEBRTC_CODEC_RED',],
       }],
     ],
   },