This is for code that prefers to use idx_t for sizes.
* lib/xalloc.h (ximalloc, xizalloc, xicalloc, xirealloc)
(xireallocarray, ximemdup, ximemdup0) [GNULIB_XALLOC]:
New decls.
(x2nrealloc): Now just a decl, as the body is moved into xmalloc.c.
* lib/xmalloc.c: Include ialloc.h.
Rename some local parameters to be consistent with the .h files.
(nonnull): New static function.
(xmalloc, xcalloc): Simplify by using nonnull.
(ximalloc, xirealloc, xireallocarray, xizalloc, xicalloc)
(ximemdup, ximemdup0): New functions.
(x2nrealloc): Moved here from xalloc.h.
* modules/xalloc (Depends-on): Add ialloc.