[libc] [llvm] [libc] Add maintainers file (PR #133471)

[Michael Jones via llvm-commits]

michaelrj-google wrote:

I've added you two as well. I think any further additions should probably be in a followup patch so this one doesn't keep growing forever.
Also I'm going to be OOO until tuesday so if everyone has approved over the weekend please merge this for me.

https://github.com/llvm/llvm-project/pull/133471