[clang] [OpenACC][CIR] Implement basic lowering for combined constructs (PR #139119)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > in that they are the only one where there are two operations for a single construct.
> 
> https://mlir.llvm.org/docs/Dialects/OpenACCDialect/#operation-categories There are other categories where a single construct leads to multiple operations. See description at the link above about the "second group". I should add combined constructs to that list.

Thanks, corrected!  I meant to more say "that different attributes and operation insertions are going to need to happen", but didn't do a good job of that.  Corrected the commit message

https://github.com/llvm/llvm-project/pull/139119