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

src/librustc_errors/lib.rs

@@ -16,6 +16,7 @@
 #![allow(unused_attributes)]
 #![feature(range_contains)]
 #![cfg_attr(unix, feature(libc))]
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(optin_builtin_traits)]
 
 extern crate atty;