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

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> > I do not see serialization/deserialization support in the patch
> 
> You mean these 2 functions? `void OMPClauseReader::VisitOMPTransparentClause(OMPTransparentClause *C) {}` and `void OMPClauseWriter::VisitOMPTransparentClause(OMPTransparentClause *C) {}`

Yes, they are empty, it is wrong. Add a test with serialization/deserilization

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