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

Author: memoryruins

src/libcore/lib.rs

@@ -92,6 +92,7 @@
 #![feature(lang_items)]
 #![feature(link_llvm_intrinsics)]
 #![feature(never_type)]
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(exhaustive_patterns)]
 #![feature(macro_at_most_once_rep)]
 #![feature(no_core)]