[clang] [flang] [llvm] [CLANG][OpenMP] Add support for OpenMP6.0 transparent clause (PR #166810)

[Krzysztof Parzyszek via llvm-commits]

https://github.com/kparzysz requested changes to this pull request.

Sorry for the delay in reviewing.

The flang changes are actually not correct---what was there before was.  The `transparent` clause takes an expression, not a constant.

https://github.com/llvm/llvm-project/pull/166810