[clang] Use cmake to find perl executable (PR #91275)

[Matthias Braun via cfe-commits]

MatzeB wrote:

Explicitly disabling the `scan-build` tests on windows now.

I think they weren't previously running there because of `REQUIRES: shell` anyway and as far as I can tell from the buildkite results it seems the `scan-build` does not work correctly on windows at the moment.

https://github.com/llvm/llvm-project/pull/91275