Restore setting of _USE_32BIT_TIME_T to 32 bit MSVC builds.

This was removed in commit cd004067,
we're not quite sure why, but there have been reports of crashes due
to AS Perl being built with it when we are not, and it certainly
seems like the right thing to do. There is still some uncertainty
as to why it sometimes fails and sometimes doesn't.

Original patch from Owais Khani, substantially reworked and
extended by Andrew Dunstan.