HAVE_IPV6
static int available_af = HAVE_IPV4 | HAVE_IPV6;
new_available_af |= HAVE_IPV6;
if (new_available_af == (HAVE_IPV4 | HAVE_IPV6))
if (!(available_afs & HAVE_IPV6)) {
int available_afs = HAVE_IPV4 | HAVE_IPV6;