MFC r320702,r320703:

r320702:

Formalize LEAPSECONDS and OLDTIMEZONES in share/zoneinfo/... as
`MK_ZONEINFO_LEAPSECONDS_SUPPORT == yes` and
`MK_ZONEINFO_OLD_TIMEZONES_SUPPORT == yes`.

Keep `LEAPSECONDS` and `OLDTIMEZONES` for backwards compatibility,
but print out a warning notifying users that they should use the new
variables, in an effort to migrate them to the variables. This is being
done mostly for automated build tools, etc, that might rely on these
variables being set. The variables will be removed in the future on
^/head, e.g., after ^/stable/12 is cut.

Relnotes: yes

r320703:

Add tests to help verify Links functionality for .../contrib/tzdata/backwards

MFC with: r320702

MFH: r310426

If you are going to be run individually to make a new timezone set
then ensure the destination directories exist.
Especially if you define OLDTIMEZONES because the mtree pass
doesn't do it for you.

MFC after: 1 week
Sponsored by: Panzura

MFH: r308671

When you select make OLDTIMEZONES=1 then you need a few added directories
to be made or the command fails

Sponsored by: panzura

MFC r289451:

Install share/zoneinfo in a deterministic way by sorting the results from find

This helps produce deterministic METALOG output

PR: 200674
Submitted by: Fabian Keil <fk@fabiankeil.de>
Reviewed by: emaste
Obtained from: ElectroBSD

MFC r287021:

Fix build when LEAPSECONDS is enabled.

MFC r271047: Avoid ./ in zoneinfo entries in METALOG

Use of "find ." resulted in METALOG entries with an extra ./ -- e.g.,
./usr/share/zoneinfo/./America/Toronto. Avoid this by using globbing
via "find *" instead.

Approved by: re
Sponsored by: DARPA, AFRL

MFC r287021:

Fix build when LEAPSECONDS is enabled.

MFC r271047: Avoid ./ in zoneinfo entries in METALOG

Use of "find ." resulted in METALOG entries with an extra ./ -- e.g.,
./usr/share/zoneinfo/./America/Toronto. Avoid this by using globbing
via "find *" instead.

Approved by: re
Sponsored by: DARPA, AFRL