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

src/librustdoc/lib.rs

@@ -17,6 +17,7 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(iterator_find_map)]
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(set_stdio)]
 #![feature(slice_sort_by_cached_key)]
 #![feature(test)]