Integrate LLVM at llvm/llvm-project@15c7e3ee1597
Integrate LLVM at llvm/llvm-project@15c7e3ee1597

Updates LLVM usage to match
[15c7e3ee1597](https://github.com/llvm/llvm-project/commit/15c7e3ee1597)

PiperOrigin-RevId: 420173575

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