[IR] Mark some visitor methods override.

Author: ImmanuelHaffner

include/mutable/IR/Operator.hpp

@@ -497,7 +497,7 @@ struct ThePreOrderOperatorVisitor : std::conditional_t<C, ConstOperatorVisitor,
 {
     using super = std::conditional_t<C, ConstOperatorVisitor, OperatorVisitor>;
     template<typename T> using Const = typename super::template Const<T>;
-    void operator()(Const<Operator> &op) {
+    void operator()(Const<Operator> &op) override {
         try { op.accept(*this); } catch (visit_skip_subtree) { return; }
         if (auto c = cast<Const<Consumer>>(&op)) {
             for (auto child : c->children())
@@ -511,7 +511,7 @@ struct ThePostOrderOperatorVisitor : std::conditional_t<C, ConstOperatorVisitor,
 {
     using super = std::conditional_t<C, ConstOperatorVisitor, OperatorVisitor>;
     template<typename T> using Const = typename super::template Const<T>;
-    void operator()(Const<Operator> &op) {
+    void operator()(Const<Operator> &op) override {
         if (auto c = cast<Const<Consumer>>(&op)) {
             for (auto child : c->children())
                 (*this)(*child);