parser: Make associated consts not limited to the binding crate.
parser: Make associated consts not limited to the binding crate.

They're associated to a struct, and we generate the struct, so it makes sense to
generate the associated constants if so.

eqrion/cbindgen,rlhunt/cbindgen,rlhunt/cbindgen,eqrion/cbindgen,eqrion/cbindgen