[llvm] [Frontend][OpenMP] Apply ompx_attribute to all allowing leaf constructs (PR #100370)

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

@jdoerfert, you added code for this clause.  Does this PR reflect the correct behavior when `ompx_attribute` is present on a compound construct?

https://github.com/llvm/llvm-project/pull/100370