Although, I fail to understand why the duplication of work done in
prewin.h/postwin.h vs. presys.h/postsys.h is needed.

No need to force use of 32-bit time_t (which doesn't exist for 64-bit
Windows), just use defaults.

But as the return type is just 32 bits, it is actually not enough for
a HANDLE anyway on a 64-bit OS. But on the other hand, this method is
private and not used on Windows at all. So just make it abort() then.