Setting TZ in set_time_zone_rule

[Eli Zaretskii]

Is there a good reason why we don't use 'putenv' in
set_time_zone_rule, and instead manipulate 'environ' directly?

Fabrice (CC'ed) reported that this causes crashes in Emacs compiled by
MSVC on Windows, because xmalloc on Windows allocates memory from a
different heap than what's used by the runtime library for 'environ'.

But even without that problem, it looks like we go out of our way to
solve a problem that is long solved by a standard library function.

What am I missing?