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

src/librustc_allocator/lib.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(rustc_private)]
 
 #[macro_use] extern crate log;