Integrate LLVM at llvm/llvm-project@81b51b61f849
Integrate LLVM at llvm/llvm-project@81b51b61f849

Updates LLVM usage to match
[81b51b61f849](https://github.com/llvm/llvm-project/commit/81b51b61f849)

PiperOrigin-RevId: 441445691

google-research/structured-additive-IR,google-research/structured-additive-IR