[clang] [llvm] [mlir] [OpenMP][OMPIRBuilder] Use runtime CC for runtime calls (PR #168608)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 approved this pull request.

Seems reasonable to me, maybe some of the Flang people have opinions

https://github.com/llvm/llvm-project/pull/168608