Cache object files, not only libraries

CI is rebuilding quite a lot of similar code. Using a cache may reduce the build time significantly, the only problem is that we use volatile machines in CI, they do not keep state, therefore the cache would have to be pushed somewhere.

ccache:
Normally it is used locally, but it could be stored on a NFS drive. The problem is that it we want parallel access to the cache. Short search shows that it is not a good idea. Only unix is supported.
sccache:
Mozilla product, it was designed exactly for our purpose. The only thing is that it assumes S3 storage, which we do not have as we do not use AWS. Supports all 3 platforms.

Solution:
We use sccache and minio as local s3 storage