[tz] [PROPOSED] Do not assume bytes have 8 bits

[Garrett Wollman]

<<On Fri, 23 Apr 2021 14:56:21 -0700, Paul Eggert via tz <tz at iana.org> said:

> Yes, quite a few CPUs like that exist in the embedded world. And 
> historically some mainframish CPUs had 9-, or even variable-width bytes. 
> I put "theoretical interest" in that zic.c commit message only because 
> as I understand it none of those CPUs are practical platforms for 
> running zic today.

POSIX since 2001 requires eight-bit bytes, so the set of platforms
this could possibly be relevant for is even smaller.  (We only made it
explicit in 2008, as I recall, but it was implicit in the requirement
that uint8_t be defined, given the requirements C99 places on such a
type when it exists.)  There was a Unisys 36-bit operating system that
was POSIX-certified for a previous edition of the standard (before the
networking interfaces were merged, which was the proximate cause of
requiring uint8_t).

-GAWollman