[llvm] [cmake][runtimes] Pass variable type for passthrough CMake options (PR #198505)

[Raul Tambre via llvm-commits]

tambry wrote:

@petrhosek Ping. I don't want to break your downstream out-of-tree things but I also don't have a way to debug that.

https://github.com/llvm/llvm-project/pull/198505