[mlir] Apply ClangTidy findings.

modernize-use-override ClangTidy check.

This warning appears on overridden virtual functions not marked with override or
final keywords or marked with more than one of virtual, override, final.

Author: akuegel

mlir/include/mlir/Pass/Pass.h

@@ -355,7 +355,7 @@ class Pass {
 template <typename OpT = void>
 class OperationPass : public Pass {
 public:
-  ~OperationPass() = default;
+  ~OperationPass() override = default;
 
 protected:
   OperationPass(TypeID passID) : Pass(passID, OpT::getOperationName()) {}
@@ -400,7 +400,7 @@ class OperationPass : public Pass {
 template <>
 class OperationPass<void> : public Pass {
 public:
-  ~OperationPass() = default;
+  ~OperationPass() override = default;
 
 protected:
   OperationPass(TypeID passID) : Pass(passID) {}
@@ -461,7 +461,7 @@ class PassWrapper : public BaseT {
   static bool classof(const Pass *pass) {
     return pass->getTypeID() == TypeID::get<PassT>();
   }
-  ~PassWrapper() = default;
+  ~PassWrapper() override = default;
 
 protected:
   PassWrapper() : BaseT(TypeID::get<PassT>()) {}