Thank you very much for your reply and for looking into this issue!
I have to admit that I don't know much about LLVM, but thanks to your explanation I now better understand the situation.
My bug report was mainly about two things:
Raising awareness that hipcc ≥ 6.0 is actually needed, even for "consumer software" like Blender, and therefore an update would be beneficial. I think that point has been made.
Solving the problem of not being able to use a recent version of Blender in the way I would like. Regarding this: is there currently a safe way to update hipcc to ≥ 6.0 without risking system instability? I wouldn’t mind installing a few packages from sid (or even experimental), but I’d like to avoid pulling in a large set of dependencies or ending up with an unbootable system. If it's possible, it might make sense to have some kind of instructions, also for other users facing this problem.
I hope my questions make sense in the context of this bug report.
Thanks again, and all the best!