Refactor OpenMP spellings via X-macro lists

[ouankou]

Summary

• Move OpenMP enum lists into shared OpenMPKinds.def and install it.
• Generate directive and clause spellings from the shared list in OpenMPIRToString.cpp, keeping special-case spellings and dynamic variants intact.
• Reduce clang-format churn and keep enum/spelling lists synchronized.

Details

• Added OPENMP_CLAUSE_EXT for custom clause spellings (unknown resolves to empty).
• Use OPENMP_DIRECTIVE_EXT for target_data_composite, task_iteration, and unknown to preserve exact spellings.
• Centralized directive/clause name mapping with getDirectiveSpelling() and getClauseSpelling() helpers.

Testing

• cmake --build build --target tester
• ctest --output-on-failure

[ouankou]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".