[llvm] Revert "[CI] Migrate to runtimes build" (PR #143612)

[George Burgess IV via llvm-commits]

gburgessiv wrote:

Thanks! I'll wait for CI to verify before landing. If https://github.com/llvm/llvm-project/pull/143597 lands before I press 'squash and merge' here, happy to wait and see if that fixes forward

https://github.com/llvm/llvm-project/pull/143612