MFH: r489819 r490082
audio/oss: unbreak in FreeBSD > 12
Unbreak port in FreeBSD 12 and 13-CURRENT. Broken most likely due to r335879.
While here:
- Add missing LIB_DEPENDS and USES for ossxmix
- Reorder some variables
PR: 233018
Reported by: sergey@akhmatov.ru
Approved by: ports-secteam (miwi)