Fix clang warnings

[victorapm]

Fix compilation warnings with clang-22

caliper-build/src/services/mpiwrap/Wrapper.cpp:225:6: warning: ‘{anonymous}::MPI_Barrier_is_wrapped’ defined but not used [-Wunused-variable]
  225 | bool MPI_Barrier_is_wrapped = false;
      |      ^~~~~~~~~~~~~~~~~~~~~~
caliper-build/src/services/mpiwrap/Wrapper.cpp:222:6: warning: ‘{anonymous}::MPI_Attr_put_is_wrapped’ defined but not used [-Wunused-variable]
  222 | bool MPI_Attr_put_is_wrapped = false;
      |      ^~~~~~~~~~~~~~~~~~~~~~~
caliper-build/src/services/mpiwrap/Wrapper.cpp:219:6: warning: ‘{anonymous}::MPI_Attr_get_is_wrapped’ defined but not used [-Wunused-variable]
  219 | bool MPI_Attr_get_is_wrapped = false;
      |      ^~~~~~~~~~~~~~~~~~~~~~~