* I expect that mlir-hlo will be a non-optional dependency of the project, so adding as a sub-module.
* IREE is an optional dependency and I'm keeping this as an out-of-tree checkout for the moment.
* The script will compute the join across both iree and mlir-hlo to find a common LLVM version.
* The script needs some more work (like a flag that says to update the version, etc). Likely needs more testing through an integrate or two.
Stella Laurenzo