Function do_thin_lto 

fn do_thin_lto<B: ExtraBackendMethods>(
    cgcx: &CodegenContext,
    prof: &SelfProfilerRef,
    shared_emitter: SharedEmitter,
    tm_factory: TargetMachineFactoryFn<B>,
    exported_symbols_for_lto: Arc<Vec<String>>,
    each_linked_rlib_for_lto: Vec<PathBuf>,
    needs_thin_lto: Vec<(String, <B as WriteBackendMethods>::ThinBuffer)>,
    lto_import_only_modules: Vec<(SerializedModule<<B as WriteBackendMethods>::ModuleBuffer>, WorkProduct)>,
) -> Vec<CompiledModule>