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

src/libtest/lib.rs

@@ -35,6 +35,7 @@
 #![feature(asm)]
 #![feature(fnbox)]
 #![cfg_attr(any(unix, target_os = "cloudabi"), feature(libc))]
+#![cfg_attr(not(stage0), feature(nll))]
 #![feature(set_stdio)]
 #![feature(panic_unwind)]
 #![feature(staged_api)]