[nll] libterm: enable feature(nll) for bootstrap

src/libterm/lib.rs

@@ -50,6 +50,7 @@
 #![cfg_attr(windows, feature(libc))]
 // Handle rustfmt skips
 #![feature(custom_attribute)]
+#![cfg_attr(not(stage0), feature(nll))]
 #![allow(unused_attributes)]
 
 use std::io::prelude::*;