add a rustc::query_stability lint

compiler/rustc_incremental/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(let_else)]
 #![feature(nll)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_middle;