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

[Mike Rice via cfe-commits]

mikerice1969 wrote:

Hi @josemonsalve2 if you want to help move this along it would be best to break this into at least three separate PRs.
1) Parsing/Sema/Serialization
2) CodeGen
3) Extension checking framework

In whatever order makes sense to you.
We've added several extension directives in our downstream so I should be able to help here if you can break these up a bit.

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