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

[Jose Manuel Monsalve Diaz via cfe-commits]

josemonsalve2 wrote:

My concern is how to split it up is I do not know a set of features that can work independently to each other. We can add the ompx infrastructure in one, but it won't be used by anything in that PR. Will that be ok? 

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