Contracts core intrinsics.

These are hooks to:

  1. control whether contract checks are run
  2. allow 3rd party tools to intercept and reintepret the results of running contracts.

compiler/rustc_mir_transform/src/promote_consts.rs

@@ -457,6 +457,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                 NullOp::AlignOf => {}
                 NullOp::OffsetOf(_) => {}
                 NullOp::UbChecks => {}
+                NullOp::ContractChecks => {}
             },
 
             Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),