virtual_oss is part of base from 15.0 onwards, so instead of depending on audio/virtual_oss for those versions, build using the base system sources instead. While here, since audio/virtual_oss' upstream has been moved to FreeBSD's GitHub, use that in GH_TUPLE. Also use the latest version. Sponsored by: The FreeBSD Foundation Reviewed by: arrowd Differential Revision: https://reviews.freebsd.org/D52593