[clang] [clang][Interp] Fix crash during `InterpStack` printing (PR #68246)

[Timm Baeder via cfe-commits]

tbaederr wrote:

> Although the previous
> implementation didn't have unittests either, so I'm not sure if we actually care that much or not.

We don't, I think I've used this function once. But I don't want to delete it either because it could come in handy in the future.


LGTM

https://github.com/llvm/llvm-project/pull/68246