Stabilize order of MonoItems in CGUs and disallow query_instability lint for rustc_monomorphize

compiler/rustc_monomorphize/src/lib.rs

@@ -1,6 +1,5 @@
 #![feature(array_windows)]
 #![feature(is_sorted)]
-#![allow(rustc::potential_query_instability)]
 
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::bug;