Separate build targets for aec3 and aec3_unittests

Bug: webrtc:8844
Change-Id: Id6a98eae19aaedc87c3f402a004f58f0290d5c28
Reviewed-on: https://webrtc-review.googlesource.com/56580
Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org>
Reviewed-by: Alex Loiko <aleloi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22173}
diff --git a/audio/BUILD.gn b/audio/BUILD.gn
index 618ec84..72b27eb 100644
--- a/audio/BUILD.gn
+++ b/audio/BUILD.gn
@@ -51,6 +51,7 @@
     "../api:libjingle_peerconnection_api",
     "../api:optional",
     "../api:transport_api",
+    "../api/audio:aec3_factory",
     "../api/audio:audio_mixer_api",
     "../api/audio_codecs:audio_codecs_api",
     "../api/audio_codecs:builtin_audio_encoder_factory",