[llvm] [Github][OpenMP] Adding rule for OpenMP label (PR #65331)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

That would get us to `clang-openmp`, `flang-openmp`, `openmp-libomp`, `openmp-libomptarget`.
Or was the idea to have the clang/flang parts as part of  *-libomp and *-libomptarget?

https://github.com/llvm/llvm-project/pull/65331