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

src/librustc_save_analysis/lib.rs

@@ -12,6 +12,7 @@
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(custom_attribute)]
+#![cfg_attr(not(stage0), feature(nll))]
 #![allow(unused_attributes)]
 
 #![recursion_limit="256"]