Convert ccache to Conan package

Although it may be a circular dependency, `ccache` should be built as a Conan package instead of an ad-hoc build.

[Conan Center Index ccache recipe](https://github.com/conan-io/conan-center-index/tree/master/recipes/ccache/all)

Start by comparing the repository's current ad-hoc ccache build with the linked Conan Center Index ccache recipe. Determine how the circular dependency affects packaging, then verify that ccache is built and consumed as a Conan package instead of through the existing ad-hoc path.

Written by the indexing model from the issue text.