[llvm] [CMake] Fix the check for Windows vs ccache (PR #137238)

[Kajetan Puchalski via llvm-commits]

https://github.com/mrkajetanp approved this pull request.

LGTM, but it's probably best to wait for @petrhosek before merging given that I'm not the maintainer for this file. Nice catch in any case!

https://github.com/llvm/llvm-project/pull/137238