Some support for platforms whose libraries do not maintain a frame pointer

Some support for platforms whose libraries do not maintain a frame pointer

For platforms on which system libraries are built with the
equivalent of -fomit-frame-pointer, i.e. do not maintain EBP, save
it in the thread structure upon entry to an exception handler, and
restore the register during call_into_lisp.

Currently for Windows on x86-64 only, where it is required.
Analogous changes had been implemented for x86, but are not included
here.

Thanks to Anton Kovalenko.