[llvm] Use `ccache-swig` if `ccache` cannot be found (PR #90624)

[David Tenty via llvm-commits]

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

LGTM

(one thing I note with this ccache support  appears directly in `llvm/CMakeList.txt`, that makes me think this doesn't work for runtimes. but I think that's out of scope for this PR)

https://github.com/llvm/llvm-project/pull/90624