[llvm] [polly] [SimpleLoopUnswitch] Generalize the notion of trivial unswitching (PR #193989)

[Ehsan Amiri via llvm-commits]

amehsan wrote:

adding @arsenm to check the changes in AMDGPU test case (We catch a seemingly missed unswitching opportunity there).

The change in the polly testcase is very simple, but still adding @Meinersbur as well.

https://github.com/llvm/llvm-project/pull/193989