[llvm] [AMDGPU] Add getCmpSelInstrCost override to re-enable SimplifyCFG speculation for vector types (PR #208043)

[Matt Arsenault via llvm-commits]

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arsenm wrote:

I don't like this lambda, and it doesn't follow the general pattern of multiplying by the instruction cost?

https://github.com/llvm/llvm-project/pull/208043