I ran some experiments, and found that tzset works on Windows, and is
required after changing the TZ environment variable from within perl.
But it did not work on MingW. Maybe there is something else needed in
the Posix module that would get it to work; I didn't investigate
The only way I could figure out how to distinguish in Perl space between
MSVC and MingW was looking at the make command. Maybe there is a better
way
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