[llvm] [AMDGPU] Add islands to StructurizeCFG (PR #201675)

[Robert Imschweiler via llvm-commits]

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ro-i wrote:

And I guess that AMDGPUUnifyDivergentExitNodes is replacing unreachable by amdgcn_unreachable because unreachable is a terminator and thus cannot be threaded to a unified exit node

https://github.com/llvm/llvm-project/pull/201675