[llvm] Add myself to CODEOWNERS (PR #66363)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> I think we need some kind of general policy on how to use this file. It might be good to start with a Discourse post about it.

I am totally happy if you want to own these files (and you've already made many good changes to them) but I agree that a post is needed about the usage.

Currently there is [`pr-subscribers-llvm-analysis`](https://github.com/orgs/llvm/teams/pr-subscribers-llvm-analysis) but no fine-grained team for a subset of files. It seems that if you want to act more like a gatekeeper of these files you will have to follow the email notifications more closely...

https://github.com/llvm/llvm-project/pull/66363