Ignore the overflow for constants

Force using the constants even on x86 where they do not fit into isize (c_int)

src/sys/reboot.rs

@@ -3,6 +3,7 @@ use libc::c_int;
 use void::Void;
 use std::mem::drop;
 
+#[allow(overflowing_literals)]
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum RebootMode {
     Halt = 0xcdef0123,