[clang] [llvm] [clang][OpenMP] Prototype #1 of directive splitting (PR #108855)

[Krzysztof Parzyszek via cfe-commits]

kparzysz wrote:

Right now it's about 400 check-clang failures for all changes together.  Adding AST nodes for directives in templates causes 12 failures (mostly in slightly differing diagnostics), adding capturing regions for all constituents will have its own share, but the majority comes from the different AST structure.

https://github.com/llvm/llvm-project/pull/108855