media-plugins/gst-plugins-libmms-1.12.3::gentoo and other packages based on gst-plugins-good log at the end of their ./configure invokation: configure: *** Orc acceleration disabled by --disable-orc. Slower code paths will be used. Should they have an "orc" use-flag?
No, they don't use any ORC code and don't need the dep or option. The warning comes from configure configuring the whole set, not just libmms, as the main package does make use of orc, and the main package does have an appropriate default enabled USE flag for that. Some individual split plugins do use orc (e.g a52dec iirc) and should have a USE flag in that case, but I think all of those do have it. There's a little chance I've missed some over time of upgrades, in which case a concrete bug report against that split package is welcome.