This function has been around since 4.4BSD but was dropped upstream in 2020. This went unnoticed when tzcode was updated. Bring it back, but prepare for removing it before 14.0 is released.
PR: 269445
MFC after: 3 days
Reported by: val@packett.cool
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D38445
* Replay 2010[acflm] which had been merged but not recorded.
* Merge 2010n.
* Reorganize (unsplit) the code to match the upstream layout.
* Merge 2022[cdefg].
MFC after: 1 week
Sponsored by: Klara, Inc.