Eliminate gcc7 compiler warnings

[lipracer]

Summary

we will get warning:`parameter ‘op’ set but not used``` when template function with empty template parameter list.

[jpienaar]

Thanks, noticed it in https://buildkite.com/mlir/mlir-core/builds/21333#98a12feb-d29c-4247-8931-3721b4291fad too.

[lipracer]

Thanks for the review.
If we use c++20, we can write verify function like this:

if constexpr (!std::tuple_size<TraitTupleT>()) const {

return success();

} else {

verifyTraits(op);

}
Unfortunately we now need to use SFINAE or Template Specialization. Maybe we can also pass Operation& with side effect instead of Operation* .
I'm not sure this change is necessary.

mlir/include/mlir/IR/OpDefinition.h

 }
 
 /// The internal implementation of `verifyRegionTraits` below that returns the
 /// result of verifying the current operation with all of the provided trait
 /// types `Ts`.
 template <typename... Ts>
 static LogicalResult verifyRegionTraitsImpl(Operation *op,
                                             std::tuple<Ts...> *) {
+  (void)op;
   LogicalResult result = success();
   (void)std::initializer_list<int>{
       (result = succeeded(result) ? Ts::verifyRegionTrait(op) : failure(),
        0)...};
   return result;
 }
 
 /// Given a tuple type containing a set of traits that contain a