Function check_and_apply_linkage 

fn check_and_apply_linkage<'ll, 'tcx>(
    cx: &GenericCx<'ll, FullCx<'ll, 'tcx>>,
    attrs: &CodegenFnAttrs,
    llty: Type<'ll>,
    sym: &str,
    def_id: DefId,
) -> Value<'ll>