Address review changes.

Co-Authored-By: Igor Matuszewski <Xanewok@gmail.com>

Author: crlf0710

src/libtest/lib.rs

@@ -22,7 +22,8 @@
 #![unstable(feature = "test", issue = "27812")]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/", test(attr(deny(warnings))))]
 #![feature(asm)]
-#![feature(libc, rustc_private)]
+#![feature(libc)]
+#![feature(rustc_private)]
 #![feature(nll)]
 #![feature(set_stdio)]
 #![feature(panic_unwind)]