Integrate LLVM at llvm/llvm-project@43d6991c2a4c
Integrate LLVM at llvm/llvm-project@43d6991c2a4c

Updates LLVM usage to match
[43d6991c2a4c](https://github.com/llvm/llvm-project/commit/43d6991c2a4c)

PiperOrigin-RevId: 398515844

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