Function structurally_same_type

fn structurally_same_type<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    a: Ty<'tcx>,
    b: Ty<'tcx>,
    ckind: CItemKind,
) -> bool

Checks whether two types are structurally the same enough that the declarations shouldn’t clash. We need this so we don’t emit a lint when two modules both declare an extern struct, with the same members (as the declarations shouldn’t clash).