[llvm] [AMDGPU][Verifier] Allow llvm.amdgcn.unreachable after cs.chain (PR #139494)

[Jay Foad via llvm-commits]

jayfoad wrote:

Verifiying that chain is followed by unreachable seems dubious in the first place. Dead code would not normally be a reason for failing verification. Why can't this be handled like any other call that happens never to return?

https://github.com/llvm/llvm-project/pull/139494