Enhance error checking in heap allocation routines on MS-Windows.

Enhance error checking in heap allocation routines on MS-Windows.

 src/w32heap.c (malloc_before_dump, malloc_after_dump)
 (malloc_before_dump, realloc_after_dump, realloc_before_dump)
 (mmap_alloc, mmap_realloc): Check for errors more thoroughly and
 set errno where appropriate to emulate CRT functions.