Integrate LLVM at llvm/llvm-project@a821df993def
Integrate LLVM at llvm/llvm-project@a821df993def

Updates LLVM usage to match
[a821df993def](https://github.com/llvm/llvm-project/commit/a821df993def)

PiperOrigin-RevId: 384224317

iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox,iree-org/iree-llvm-sandbox