rem: int res = argmatch (arg, arglist, vallist, valsize);
add: ptrdiff_t res = argmatch (arg, arglist, vallist, valsize);
context: __xargmatch_internal (const char *context,		      const char *arg, const char *const *arglist,		      const char *vallist, size_t valsize,		      argmatch_exit_fn exit_fn){  int res = argmatch (arg, arglist, vallist, valsize);  if (res >= 0)    /* Success. */    return res;  /* We failed.  Explain why. */  argmatch_invalid (context, arg, res);  argmatch_valid (arglist, vallist, valsize);  (*exit_fn) ();  return -1; /* To please the compilers. */}