[llvm] [CMake] enable CMP0144 policy if available (PR #96589)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> @MaskRay are the warnings being caused by `mlir/lib/Target/LLVM/CMakeLists.txt`? Because AFAICT `mlir/lib/Target/LLVM/CMakeLists.txt` is not really affected by the change of policy because the `*_ROOT` variable in question is: `CUDAToolkit_LIBRARY_ROOT`, which is defined by `find_package(CUDAToolkit)` [(see `CUDAToolkit_LIBRARY_ROOT`)](https://cmake.org/cmake/help/latest/module/FindCUDAToolkit.html#result-variables) and not really a `<PACKAGENAME>_ROOT` variable.

The warning is from top-level CMakeLists.txt. I think this PR is safe:)

https://github.com/llvm/llvm-project/pull/96589