[llvm] [BPF] Support for `DW_TAG_variant_part` in BTF generation (PR #155783)

[Michal R via llvm-commits]

vadorovsky wrote:

> a union with additional member for discriminator

> This will make the BTF format consistent with the existing practice.

Alright, I will go forward with the union and offsets then. Hopefully I can get it working by tomorrow.

> For non-BTF, we probably cannot do much in llvm and pahole needs to do above conversion.

Yes, and I'm willing to try implementing that myself in pahole, once this PR is merged, unless there is someone else already planning such work.

https://github.com/llvm/llvm-project/pull/155783