[mlir] Fix warnings

This patch fixes:

  include/c++/14/bits/unique_ptr.h:93:2: error: delete called on
  non-final '(anonymous namespace)::MPICHImplTraits' that has virtual
  functions but non-virtual destructor
  [-Werror,-Wdelete-non-abstract-non-virtual-dtor]

Author: kazutakahirata

mlir/lib/Conversion/MPIToLLVM/MPIToLLVM.cpp

@@ -62,6 +62,8 @@ class MPIImplTraits {
 
   explicit MPIImplTraits(ModuleOp &moduleOp) : moduleOp(moduleOp) {}
 
+  virtual ~MPIImplTraits() = default;
+
   ModuleOp &getModuleOp() { return moduleOp; }
 
   /// Gets or creates MPI_COMM_WORLD as a Value.
@@ -96,6 +98,8 @@ class MPICHImplTraits : public MPIImplTraits {
 public:
   using MPIImplTraits::MPIImplTraits;
 
+  virtual ~MPICHImplTraits() = default;
+
   Value getCommWorld(const Location loc,
                      ConversionPatternRewriter &rewriter) override {
     static constexpr int MPI_COMM_WORLD = 0x44000000;
@@ -152,6 +156,8 @@ class OMPIImplTraits : public MPIImplTraits {
 public:
   using MPIImplTraits::MPIImplTraits;
 
+  virtual ~OMPIImplTraits() = default;
+
   Value getCommWorld(const Location loc,
                      ConversionPatternRewriter &rewriter) override {
     auto context = rewriter.getContext();