[llvm] [IR2Vec] Initial infrastructure for MIR2Vec (PR #161463)

[S. VenkataKeerthy via llvm-commits]

svkeerthy wrote:

### Merge activity

* **Oct 7, 8:43 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/161463).


https://github.com/llvm/llvm-project/pull/161463