Function forward_declare_type 

pub fn forward_declare_type(type_name: &str, decl_type: u32) -> TypeWriteResult

Reserve type_name in the local til as an incomplete aggregate (tinfo_t::create_forward_decl), without a body. decl_type is a type_t (BTF_STRUCT/BTF_UNION/BTF_ENUM) selecting the aggregate kind. code is the raw tinfo_code_t (0 = ok); no TEDIT_* pre-failure, since there is no existing type to load first.