gethostbyaddr_async
struct asr_query *gethostbyaddr_async(const void *, socklen_t, int, void *);
as = gethostbyaddr_async(addr, len, af, NULL);
DEF_WEAK(gethostbyaddr_async);
as = gethostbyaddr_async(&in, sizeof(in), family, asr);
PROTO_NORMAL(gethostbyaddr_async);