bindings: Make ADIOS2_HAVE_MPI_F definition private to Fortran sources

bindings/Fortran/CMakeLists.txt

@@ -51,13 +51,13 @@ target_link_libraries(adios2_f PRIVATE adios2)
 
 
 if(ADIOS2_HAVE_MPI)
+  target_compile_definitions(adios2_f PRIVATE "$<$<COMPILE_LANGUAGE:Fortran>:ADIOS2_HAVE_MPI_F>")
   target_sources(adios2_f PRIVATE
     modules/adios2_adios_init_mod_mpi.f90
     modules/adios2_io_open_mod_mpi.f90
     f2c/adios2_f2c_adios_mpi.cpp
     f2c/adios2_f2c_io_mpi.cpp
   )
-  target_compile_definitions(adios2_f PUBLIC ADIOS2_HAVE_MPI_F)
   target_link_libraries(adios2_f PRIVATE MPI::MPI_Fortran MPI::MPI_C)
 endif()