[clang] [OpenMP] Introduce support for OMPX extensions and taskgraph frontend (PR #66919)

[Jose Manuel Monsalve Diaz via cfe-commits]

josemonsalve2 wrote:

I mean front end code minus the taskgraph directive part. Just the part that allows for ompx to be used. 

If we include the taskgraph, then it will generate code that cannot be linked. So it would be a PR that will not work for programs. 

https://github.com/llvm/llvm-project/pull/66919