liveness: Use newtype_index for Variable and LiveNode

compiler/rustc_passes/src/lib.rs

@@ -5,6 +5,8 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(const_fn)]
+#![feature(const_panic)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(or_patterns)]