[llvm] [CMake] enable CMP0147 policy if available (PR #109150)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> CC @mstorsjo who might be able to help

Sorry, no idea what has happened here - I'd suggest trying to rebase on top of latest main and retrying.

https://github.com/llvm/llvm-project/pull/109150