[llvm] AMDGPU/GlobalISelDivergenceLowering: select divergent i1 phis (PR #78482)

[Pierre van Houtryve via llvm-commits]

https://github.com/Pierre-vh commented:

I just have some nits to make the pass easier to follow, as I think this is going to be a core component of the GISel flow so the code should be as approachable as possible to encourage contributions and make bugfixing easier

https://github.com/llvm/llvm-project/pull/78482