rustdoc: test ignoring rustc lints in CLI

Author: notriddle

tests/rustdoc-ui/lints/unused.rs

@@ -1,11 +1,13 @@
+//@ revisions: unused_attr unused_cli
+//@[unused_cli] compile-flags: -Dunused_imports
 //@ check-pass
 
 // This test purpose is to check that unused_imports lint isn't fired
 // by rustdoc. Why would it? Because when rustdoc is running, it uses
 // "everybody-loops" which replaces parts of code with "loop {}" to get
 // huge performance improvements.
 
-#![deny(unused_imports)]
+#![cfg_attr(unused_attr, deny(unused_imports))]
 
 use std::fs::File;