LLVM ist a mess

Oh my goodness no. LLVM needs to decide what it wants to be, IMHO. If they are a compiler, then each version can do, what it likes – as long as it produces executable programs without any bugs due to its internals.

If they want to offer a libllvm (and all the other wonderful libraries like libclang), with a SONAME, that indicates it is stable, they need to get their act together. Or make it impossible (or at least a manual downstream patch) to do dynamic linking (which they do not). Apart from that: even static linking caused issues in the past. When I linked LLVM statically, I still ended up having issues with executed workloads, that brought their own (sometimes statically linked) versions of LLVM. I have to admit, that I never went for the deep dive into these issues, since I am not given time for that during my day job. But I do have to keep the workloads running. So far that meant either manually "fixing" the LLVM builds (I will not claim these to be universally applicable fixes) or pinning the deployed LLVM version until we could work something out with our various upstreams.

(Side note: building LLVM across platforms is not fun. LLVM constantly breaks one build or another. I am sure Sylvestre (who's behind apt.llvm.org) and others beyond myself could attest to that. So even your "just bundle it" solution falls flat on its face right away.)