It is the social problem of having people show up and grind maintenance work to just make it compile. Which means other questions are left untouched. It is approximately zero sum.

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.