[llvm-branch-commits] [OpenMP] Fixes for compound members of irreducible regions (PR #225689)

[Julian Brown via llvm-branch-commits]

https://github.com/jtb20 created https://github.com/llvm/llvm-project/pull/225689

In processed taskgraphs, we permit irreducible regions to contain any
other region type, so it's legal to have a parallel or sequential region
(or even another irreducible region) as a child of that region.

This patch fixes some bugs concerning such cases, and adds two new tests.

Assisted-By: Claude Opus 5