xalloc: adjust to malloc ptrdiff_t change * lib/xmalloc.c (HAVE_GNU_CALLOC, HAVE_GNU_MALLOC, HAVE_GNU_REALLOC): Remove. (xmalloc, xrealloc, xcalloc): Simplify by assuming GNU behavior. * modules/xalloc (Depends-on): Add calloc-gnu, malloc-gnu, realloc-gnu.