message: testing: Fix Install.CMake.C test to use correct MPI component
  The C test should use `MPI::MPI_C`, not `MPI::MPI_CXX`.
diff: @@ -11,7 +11,7 @@ find_package(adios2 REQUIRED)
  if(ADIOS2_HAVE_MPI)
  find_package(MPI REQUIRED)
  set(src main_mpi.c)
  - set(mpilib MPI::MPI_CXX)
  + set(mpilib MPI::MPI_C)
  set(mpiexec ${MPIEXEC_EXECUTABLE} ${MPIEXEC_EXTRA_FLAGS})
  else()
  set(src main_nompi.c)
  