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

Author: memoryruins

src/libunwind/lib.rs

@@ -13,6 +13,7 @@
 
 #![feature(cfg_target_vendor)]
 #![feature(link_cfg)]
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(staged_api)]
 #![feature(unwind_attributes)]
 #![feature(static_nobundle)]