[tz] suggestion: split "backward" into "backward" and "deprecated"

[Paul Eggert]

On 5/4/20 8:16 PM, Philip Paeps wrote:

> It looks like we install the files rather than links.  Or I've botched something
> on the test machine I looked at (which is not unlikely).

If you're installing files then that should get fixed. In tzdb on my Fedora 31
platform (ext4 filesystem with 4 KiB blocks), 'make install' creates a zoneinfo
directory that 'du' reports consumes 1800 KiB, as opposed to the 1776 KiB
consumed for the same directory with 'make BACKWARD="" install'. The 24 KiB
difference comes mostly from the five extra directories implied by 'backward'
(Brazil, Canada, Chile, Mexico, US) each of which consume 4 KiB; the rest comes
from the larger tzdata.zi file (108 vs 112 KiB allocated, due to the extra -L
lines).

>>> Or they can trivially patch the build system not to install backward zones.
>>
>> Well, there used to be a build option for that in the base system, but
>> somebody just took it out...
> 
> Easy enough to put back if someone yells about it.

Might make sense to put it back in (if only for compatibility with older FreeBSD
systems where TZ='W-SU' gave you UTC :-).