[tz] make error

[Paul Eggert]

On 2023-11-16 21:04, Robert Elz via tz wrote:
> This does suggest though that for something like tzcode, which is used
> everywhere, requiring C99 anytime soon might be a mistake

Not sure this particular example suggests that, as Alois merely needs to 
compile with --std=gnu11 (or --std=gnu99 or -DPORT_TO_C89 or whatever). 
C99 came out decades ago, support for the C99 features that tzcode uses 
by default is reasonably universal now, and there's always -DPORT_TO_C89 
for any museum pieces.

For what it's worth, I help maintain other packages like GNU coreutils 
that are quite widely ported. Coreutils started using these C99 features 
in 2009 and it hasn't been a significant porting problem in practice.