[tz] Undoing the effect of the new alike-since-1970 patch

[Tom Lane]

Paul Eggert via tz <tz at iana.org> writes:
> So I propose we add a Makefile or similar build-time option to let tzdb 
> users have it either way. Set the flag one way, and it will be as if the 
> recently-proposed changes did not occur. Set it the other way, and 
> you'll get the changes.

Works for me, as long as it's possible to get the formerly-default
zone data (that is, without the old backzone additions).

> This will be similar to our vanguard/rearguard support, which helped 
> address a similar disagreement back in 2018. We could even control 
> things via the existing vanguard/rearguard build-time option; that might 
> be simpler. If you have ideas about what the the option's specific 
> effects should be, please let me know.

Please *do not* tie this to vanguard/rearguard.  The fact that tzdb
consumers might disagree with your revisions to the data classification
doesn't mean that they want to get locked into obsolete file formats.

			regards, tom lane