Make resolutions a query.

compiler/rustc_metadata/src/creader.rs

@@ -51,6 +51,12 @@ pub struct CStore {
     unused_externs: Vec<Symbol>,
 }
 
+impl std::fmt::Debug for CStore {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CStore").finish_non_exhaustive()
+    }
+}
+
 pub struct CrateLoader<'a> {
     // Immutable configuration.
     sess: &'a Session,