[llvm] [LLVM][DebugInfo] Allow ExtraData field to be a node reference (PR #165023)

[Vladislav Dzhidzhoev via llvm-commits]

dzhidzhoev wrote:

> > That said, this area does seem poorly specified. The langref only briefly mentions the extraData field and the verifier doesn't complain. I think in an ideal world the verifier would have complained about the tuple extraData, rather than hitting an assert later.
> 
> Verifier didn't complain about the tuple `extraData` because that is a valid IR if the `tag` in `!DIDerivedType` is `DW_TAG_ptr_to_member_type` and is handled correctly in the backend.

But !4 in the given example isn't a tuple, is it? Is there something that prevents us from adding such check?

https://github.com/llvm/llvm-project/pull/165023