Ensure 8-byte aligned memory allocation on MS-Windows 9X

Ensure 8-byte aligned memory allocation on MS-Windows 9X

* src/w32heap.c (init_heap): Redirect malloc, realloc, and free to
special functions on Windows 9X.  Refuse to dump Emacs on Windows 9X.
(malloc_after_dump_9x, realloc_after_dump_9x)
(free_after_dump_9x): New functions.  (Bug#22379)  See also
http://lists.gnu.org/archive/html/emacs-devel/2016-01/msg00852.html
for more details about the original problem.

* nt/inc/ms-w32.h (malloc_after_dump_9x, realloc_after_dump_9x)
(free_after_dump_9x): Add prototypes.

Copyright-paperwork-exempt: yes