[llvm] [SandboxIR] Implement UndefValue (PR #107628)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Please ignore me:
https://github.com/llvm/llvm-project/blob/de88d7db7b77141297fbb5638ee1e18d1fba53b8/llvm/include/llvm/IR/Constants.h#L1433

https://github.com/llvm/llvm-project/pull/107628