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

[Vlad Serebrennikov via llvm-commits]

Endilll wrote:

I'd like to second Tobias' feedback. `CMAKE_<LANG>_COMPILER_LAUNCHER` has been around since CMake 3.4, while our minimum requirement in 3.20, so there are no compatibility reasons to do this.

On top of that, I think compiler launcher should be treated as a part of toolchain. That is, if present, it should be either set by user on the command line, or in a toolchain file. Notably, we shouldn't try to be smart about it after `project()` is called, like unofficial (yet Kitware-hosted) documentation has been saying for at least 6 years for `CMAKE_<LANG>_COMPILER`: https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#method-3-avoid-use-set

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