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

[David Tenty via llvm-commits]

daltenty wrote:

> I don't this we should add more stuff to LLVM_ENABLE_CCACHE. I think people should use CMAKE_C/CXX_COMPILER_LAUNCHER instead.

Thanks for the tip. Reading the CMake docs that seems a reasonable solution. 

Should we make mention of this in https://github.com/llvm/llvm-project/blob/main/llvm/docs/CMake.rst and/or issue a message about this option being deprecated? Those docs are what originally led us down this path.

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