Enable const_fn in newtype test

Author: JamesHinshelwood

src/librustc_target/lib.rs

@@ -24,6 +24,7 @@
 #![feature(box_syntax)]
 #![feature(nll)]
 #![feature(slice_patterns)]
+#![feature(const_fn)]
 
 #[macro_use]
 extern crate bitflags;

src/test/run-pass-fulldeps/newtype_index.rs

@@ -1,4 +1,4 @@
-#![feature(rustc_attrs, rustc_private, step_trait)]
+#![feature(rustc_attrs, rustc_private, step_trait, const_fn)]
 
 #[macro_use] extern crate rustc_data_structures;
 extern crate rustc_serialize;