[libclc] [llvm] [libclc][CMake] Use clang/llvm-ar on Windows (PR #186726)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

You could possibly try defining `CMAKE_CLC_COMPILER` yourself, but it would need to be present before your root CMake invocation.

https://github.com/llvm/llvm-project/pull/186726