Integrate LLVM at llvm/llvm-project@18bf42c0a688
Integrate LLVM at llvm/llvm-project@18bf42c0a688

Updates LLVM usage to match
[18bf42c0a688](https://github.com/llvm/llvm-project/commit/18bf42c0a688)

PiperOrigin-RevId: 428715749

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