Use simpler way to print function pointers

Use simpler way to print function pointers

The module code can’t possibly work on weird platforms where
function pointers are wider than data pointers, so there’s no need
to bother with the stackoverflow-like approach that is intended
only for portability to such platforms.  Besides, the
stackoverflow-like approach does not work well on weird platforms
where CHAR_BIT is not a multiple of 4.
* src/lisp.h (pMx): New macro.
* src/print.c (data_from_funcptr) [HAVE_MODULES]: New function.
(print_vectorlike) [HAVE_MODULES]: Use it.
(print_object): Make sure buf is big enough for this.