fn generate_lto_work<B: ExtraBackendMethods>(
    cgcx: &CodegenContext<B>,
    needs_fat_lto: Vec<FatLtoInput<B>>,
    needs_thin_lto: Vec<(String, B::ThinBuffer)>,
    import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>
) -> Vec<(WorkItem<B>, u64)>