Function gio_sys::g_output_stream_writev_async

pub unsafe extern "C" fn g_output_stream_writev_async(
    stream: *mut GOutputStream, 
    vectors: *const GOutputVector, 
    n_vectors: size_t, 
    io_priority: c_int, 
    cancellable: *mut GCancellable, 
    callback: GAsyncReadyCallback, 
    user_data: gpointer
)

This is supported on crate feature v2_60 only.