Function GC_unregister_disappearing_link 

pub unsafe extern "C" fn GC_unregister_disappearing_link(
    arg1: *mut *mut c_void,
) -> c_int

Undoes a registration by either GC_register_disappearing_link() or GC_general_register_disappearing_link(). Returns 0 if link was not actually registered (otherwise returns 1).