BTF_FWD_UNION
case BTF_FWD_UNION: {
t->info = btf_type_info(BTF_KIND_FWD, 0, fwd_kind == BTF_FWD_UNION);
(cand_kind == BTF_KIND_UNION && fwd_kind != BTF_FWD_UNION))
id = btf__add_fwd(btf, "union_fwd", BTF_FWD_UNION);