add a rustc::query_stability lint

compiler/rustc_session/src/lib.rs

@@ -3,6 +3,7 @@
 #![feature(min_specialization)]
 #![feature(once_cell)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_macros;