The Fedora dist-git repository for llvm has all the latest changes that are needed to update RHEL to LLVM 22. There is a script called centos-sync.sh in the rawhide branch of fedora dist-git.  If you run this script it will correctly copy all the necessary files from Fedora rawhide into a Centos Stream git checkout in a directory called llvm-centos.  You can just commit the files there and then submit a PR.  Here is how to run the script:

./centos-sync.sh --centos-branch c9s

Note that if RHEL-140410 is completed you need to pass the --no-bundle option to the script.