Being a good citizen: New ESMA_cmake include and External users

[mathomp4]

This is a question/discussion for @rmontuoro (and maybe @LiamBindle?).

Soon-ish, I will be including a new file, esma_cpack.cmake in our ESMA_cmake repo. Now, because of ecbuild, I can't just "hide" it inside of our esma.cmake omnibus file where it wouldn't matter. Rather, I'll have to add to the end of MAPL's CMakeLists.txt file a la:

...
# Piggyback that file into install
install(
   FILES ${PROJECT_BINARY_DIR}/.gitignore
   DESTINATION ${CMAKE_INSTALL_PREFIX}
   )

ecbuild_install_project (NAME MAPL)

# CPack
include(esma_cpack OPTIONAL)

Where those last two lines are the important ones. Now, my hope is that maybe the OPTIONAL is enough to get by, but there is stuff in CMakeLists that @rmontuoro added like:

...
# build as standalone project
if (NOT COMMAND esma)
  include (esma OPTIONAL)
endif ()

if (NOT COMMAND esma)

  if (SKIP_MEPO)
    message (FATAL_ERROR "ESMA not found")
  else ()
...

Now, I'll work with @weiyuan-jiang to try it out with UFS first, but I thought I'd lean on @rmontuoro's experience and knowledge to see if you can think of more CMake protection that might be needed?

[LiamBindle]

I think we should be okay on our end. We include ESMA_cmake in GCHP so we'll get that new module when we update ESMA_cmake (unless I've misunerstanding something here). Thanks for the ping.