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

[Michal R via llvm-commits]

vadorovsky wrote:

> Do you plan to wrap this up?

I do, but I'm blocked by Rust which is emitting `undef` for all static variable definitions. Still trying to figure out a proper fix on Rust's side. If you prefer, I can close or mark this PR as draft until I sort it out.

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