Integrate LLVM at llvm/llvm-project@21ef1cac1372
Integrate LLVM at llvm/llvm-project@21ef1cac1372

Updates LLVM usage to match
[21ef1cac1372](https://github.com/llvm/llvm-project/commit/21ef1cac1372)

PiperOrigin-RevId: 483649246

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