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

Author: memoryruins

src/libproc_macro/lib.rs

@@ -31,6 +31,7 @@
        test(no_crate_inject, attr(deny(warnings))),
        test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]
 
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(rustc_private)]
 #![feature(staged_api)]
 #![feature(lang_items)]