--- a/src/bootstrap/lib.rs
+++ a/src/bootstrap/lib.rs
@@ -273,6 +273,7 @@
         RefCell<HashMap<TargetSelection, HashMap<String, (&'static str, PathBuf, Vec<String>)>>>,
 }
 
+#[allow(dead_code)]
 #[derive(Debug)]
 struct Crate {
     name: Interned<String>,