Function qsort_r 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn qsort_r(
    base: *mut c_void,
    nel: size_t,
    width: size_t,
    compar: Option<extern "C" fn(*const c_void, *const c_void, *mut c_void) -> c_int>,
    arg: *mut c_void,
)

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/qsort_r.html.