No, that has nothing to do with any of the problems julia faces. Julia's LLVM is just regular LLVM with some patches that are usually upstreamed. The Julia team is pretty good at keeping up with upstream LLVM.
I mean, fundamentally, keeping a C++ abi backwards compatible is a horror story. It like, just doesn't work, for non-trivial projects. So LLVM breaks all the time.
https://docs.julialang.org/en/v1/devdocs/llvm/
Julia got like 12 custom LLVM passes. They are deep into the LLVM. And they seems to include C++ headers from the LLVM project, not using the C api.
In practice you'd want insider maintainers in the LLVM project to guard your dependency like it would have been an in tree front-end.
I say this as one of the devs that usually do the work of keeping up the latest LLVM.