[llvm] [SimplifyCFG] Skip threading if the target may have divergent branches (PR #100185)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

This may have broken the AMDGPU hip-clang buildbot: https://lab.llvm.org/buildbot/#/builders/123/builds/2677

https://github.com/llvm/llvm-project/pull/100185