[flang-commits] [flang] [flang][OpenMP] Implement getOpenMPVersion helper function, NFC (PR #90086)

[Tom Eccles via flang-commits]

https://github.com/tblah approved this pull request.

nit: maybe instead of `llvm_unreachable`, we could return `std::nullopt` or some sentinel value. It would be unfortunate if we got into a situation where every mlir file in the test suite needed to have this attribute added to the module.

But it is hard to comment without seeing where this will be used so LGTM whether or not you decide to change.

https://github.com/llvm/llvm-project/pull/90086