[llvm] AMDGPU: Preserve carry-out dead flag in V_ADD_CO_U32 custom inserter (PR #225736)

[Frederik Harwath via llvm-commits]

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frederik-h wrote:

> I don't actually understand why the VOP3 handling was here in the first place. The VOP3 cases aren't handled in the switch.
I also found it confusing. Makes sense to fix this later.

https://github.com/llvm/llvm-project/pull/225736