[clang] [llvm] [Frontend] Add leaf constructs and association to OpenMP/ACC directives (PR #83625)

[Kiran Chandramohan via cfe-commits]

https://github.com/kiranchandramohan approved this pull request.

> Add members "leafs" and "association" to .td describing OpenMP/ACC directives: "leafs" are the leaf constructs for composite/combined constructs, and "association" is the source language construct to which the directive applies (e.g. loop, block, etc.)

Could you clarify that these are terminology used in the OpenMP standard?

Great work @kparzysz.

https://github.com/llvm/llvm-project/pull/83625