message: update for rustc changes: treat new MIR commands as NOP
diff: @@ -127,6 +127,9 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  self.deallocate_local(old_val)?;
  }
  + // Validity checks. Not yet implemented.
  + Validate(_, _) => {}
  +
  // Just a borrowck thing
  EndRegion(..) => {}
  