#if RETSIGTYPE != void
That isn't C, and MSVC properly refuses to compile it.
Introduced new Py_RETURN_FROM_SIGNAL_HANDLER macro in pyport.h
to expand to the correct thing based on RETSIGTYPE.  However,
only void is ANSI!  Do we still have platforms that return int?
The Unix config mess appears to #define RETSIGTYPE by magic
without being asked to, so I assume it's "a problem" across
Unices still.