Some final touches to ensure ./x.py test --stage 0 src/lib* works

src/libcore/tests/num/uint_macros.rs

@@ -98,6 +98,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(not(stage0))]
     fn test_reverse_bits() {
         assert_eq!(A.reverse_bits().reverse_bits(), A);
         assert_eq!(B.reverse_bits().reverse_bits(), B);