fn set_members_of_composite_type<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    composite_type: Ty<'tcx>,
    composite_type_metadata: &'ll DICompositeType,
    member_descriptions: Vec<MemberDescription<'ll>>,
    common_members: Option<&Vec<Option<&'ll DIType>>>
)