[clang] [OpenACC] Implement 'var' parsing correctly, support array sections (PR #77617)

[Alexey Bataev via cfe-commits]

alexey-bataev wrote:

> @alexey-bataev : In particular I'd like to make you aware of what I've done here, since this is similar to the work you've done before/will affect it. It is currently my thought to make the OMPArraySectionExpr type a generic 'ArraySectionExpr' type in the not-so-distant future (PERHAPS with the OMP and OpenACC types inheriting from it? But perhaps those types aren't necessary), so I anticipate you'll be seeing stuff like this in the future.

Sure. I agree that better to reuse the existing implementation rather than add something new here. I don't have strong preferences, if it is better deriving OpenMP/OpenACC specific types or just have some "structural/functional" check. It depends on how many changes are required.

https://github.com/llvm/llvm-project/pull/77617