[llvm] [libc++] Fix CODEOWNERS file for libc++ (PR #65344)

[Tom Stellard via llvm-commits]

tstellar wrote:

The reason we are using the CODEOWNERS file to achieve 1), is because it sends a notification with a full summary of the PR when it is first created.  Any label based notification scheme (like we have for issues) is going to subscribe people to the issue after it is created, so they won't get the PR creation notification, but they will get a notification for all other updates to the PR.

I wonder in general how many people want to subscribe to PRs, but don't want to be added as a reviewer?  If this is a small group, we could do a hybrid approach where we use the CODEOWNERS file as it is intended to add reviewers and then do a label based notification system for people who only want to subscribe.   Either way though, I think we are going to end up needing two groups, one for reviewers and one for subscribers.

https://github.com/llvm/llvm-project/pull/65344