fixes #4 add cmake fortran module directory using ecbuild method

[suvarchal]

fixes #4 by adding (with hints from fckit and eccodes)

if(ECBUILD_INSTALL_FORTRAN_MODULES)
    install( DIRECTORY ${CMAKE_Fortran_MODULE_DIRECTORY}/${CMAKE_CFG_INTDIR}/
             DESTINATION ${INSTALL_INCLUDE_DIR}
             COMPONENT modules)
endif()

to src/multio/CMakeLists.txt.

I considered following working(tested) options before deciding which CMakeLists.txt to add the above snippet to:

• To root dir CMakeLists.txt, but elegance of using modular ecbuild cmake functions is lost and importantly fortran modules from tests are also installed, which is not desirable.
• To CMakeLists.txt in both src/multio/api and src/multio/server as they both have Fortran modules, but thought it is redundant as CMAKE_Fortran_MODULE_DIRECTORY is only needed to be set once for project and having at both places is repetition.

[FussyDuck]

All committers have signed the CLA.

[dsarmany]

Thank you for this. I suggest a slight modification to the proposed change to make it more consistent with other ECMWF packages:

if( HAVE_FORTRAN AND ECBUILD_INSTALL_FORTRAN_MODULES )
    install( DIRECTORY ${CMAKE_Fortran_MODULE_DIRECTORY}/${CMAKE_CFG_INTDIR}
             DESTINATION module/multio
             COMPONENT modules )
endif()

Once the change is updated, I'm happy to merge it. (Alternatively, I can also introduce the change to the develop branch outside this PR if that is requested.)

[dsarmany]

Close this as it is fixed already on both develop and 2.1.