[llvm] [SandboxIR] Implement UnaryInstruction class (PR #101541)

[Arthur Eubanks via llvm-commits]

https://github.com/aeubanks commented:

I'm not sure this is useful. UnaryInstruction doesn't expose any new common methods for people to use, and passes aren't going to check for UnaryInstruction. At least the LLVM IR UnaryInstruction has some allocation size logic.

https://github.com/llvm/llvm-project/pull/101541