src/libexec/rc/rc.d/localpkg, branch release/12.3.0

MFC r352999:

2020-08-27T19:37:28+00:00

Rename etc/rc.d/abi to etc/rc.d/linux; after moving out the SysV IPC stuff
it's entirely linux-specific.

MFC r353054:

Add rcvar back to the linux rc script.  Without it it was enabled
unconditionally.

Sponsored by:	The FreeBSD Foundation

MFC r352836:

2020-08-27T19:35:02+00:00

Move the SysV IPC stuff out of the 'abi' rc script, into a new one:
'sysvipc' - it has nothing to do with ABIs, and I'd like to later
rename 'abi' to 'linux', which better describes its purpose and also
matches the rcvar name.

Sponsored by:	The FreeBSD Foundation

Move the rc framework out of sbin/init into libexec/rc.

2018-10-17T16:49:11+00:00

The reasons for this are forward looking to pkgbase:
 * /sbin/init is a special binary; try not to replace it with
   every package update because an rc script was touched.
   (a follow-up commit will make init its own package)
 * having rc in its own place will allow more easy replacement
   of the rc framework with alternatives, such as openrc.

Discussed with:		brd (during BSDCam), kmoore
Requested by:		cem, bz
PR:			231522
Approved by:		re (gjb)