Fix tests

src/libcore/mem/mod.rs

@@ -1009,6 +1009,8 @@ pub const fn discriminant<T>(v: &T) -> Discriminant<T> {
 /// # Examples
 ///
 /// ```
+/// # #![feature(never_type)]
+///
 /// use std::mem;
 ///
 /// enum Void {}

src/test/ui/consts/const-variant-count.rs

@@ -1,6 +1,7 @@
 // run-pass
 #![allow(dead_code)]
 #![feature(variant_count)]
+#![feature(never_type)]
 
 use std::mem::variant_count;