Local binary cache

[GPMueller]

Similar to the caches of conan or vcpkg, we should at some point add the ability to use cached builds:

• when the dependency of a target is not found, it is searched for in the cache
• to put a target in the cache, a specific command must be called
• the cache folder structure could look something like ~/.clang-build/cache/projectname/targetversion/targetname/buildtype/

Questions:

• how to specify dependency versions? Maybe like Python, e.g. Eigen>=0.0.1?
• can individual targets be placed into the cache or only whole projects?

This is also related to the current ideas around bundling and redistributable packages, see PR #98 and https://clang-build.readthedocs.io/en/latest/user_guide/bundling.html

[GPMueller]

Maybe it would be smarter to leave the packaging aspect to tools specialized to this task.

It would be easy enough to write a clang-build.py script that generates a project with targets pointing to the local conan cache. The user could then conan install whatever versions of libraries they want and depend on them in clang-build targets. This could be provided as a kind of "real-world example".