[llvm] [UniformityAnalysis] Add test for missed cycle exit PHI divergence (PR #216100)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

Closing it. The PR https://github.com/llvm/llvm-project/pull/216296 has included this test along with the fixup.

https://github.com/llvm/llvm-project/pull/216100