Oh yeah sorry I'm not blaming cling at all. It might be easier if cling were completely baked into llvm, but obviously there's a debate to be had about that. I see today you can embed cling[1] which is a lot easier than when you had to use ROOT. Still not the simplest thing though.
[1] https://cdn.rawgit.com/root-project/cling/master/www/index.h... See "Embedding Cling"