[llvm] [MIR] Serialize virtual register flags (PR #110228)

[Akshat Oke via llvm-commits]

optimisan wrote:

### Merge activity

* **Oct 14, 4:48 AM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/110228).


https://github.com/llvm/llvm-project/pull/110228