Function pthread_key_create 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pthread_key_create(
    key_ptr: *mut pthread_key_t,
    destructor: Option<extern "C" fn(value: *mut c_void)>,
) -> c_int

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