Which version are you building?
Not putting my nose in the code much but:
- Yes some of the CAD importer cannot be built from source as we cannot ship the 3rd party library for people to rebuild
- IFC engine lib should be removed in 5.3, we basically stop supporting it using the IFC library and switch to support with the library we use for other CAD formats. So that does not change the fact you cannot rebuild CAD library from source, but the WITH_IFC_ENGINE_LIB should disappear.