Bump externals/llvm-project from ac378c2 to cfac8df

Bumps [externals/llvm-project](https://github.com/Xilinx/llvm-project) from `ac378c2` to `cfac8df`.
- [Commits](Xilinx/llvm-project@ac378c2...cfac8df)

---
updated-dependencies:
- dependency-name: externals/llvm-project
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>