[llvm] [AMDGPU][GlobalISel] Fix VCC s1 phi instruction selection failure (PR #184632)

[Petar Avramovic via llvm-commits]

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petar-avramovic wrote:

> // VCC S1 phis cannot be instruction-selected.

This is true.
They should be lowered in amdgpu-global-isel-divergence-lowering.
If there are actual problems need to fix them in amdgpu-global-isel-divergence-lowering.

https://github.com/llvm/llvm-project/pull/184632