GitHub has the weird restriction that builders in a branch can only
access their own cache as well as the one from "master". Which means
PRs cannot use each others CCache. Therefore the master build was
also updating the cache.
This also means we'll have to compile clang there as well, just so that
the cache can get updated. As with the PR build, the resulting binaries
aren't packaged.
I've also fixed the name for the windows cache, build-pr was using
ccache-win, but build.yml was using win-ccache
This commit also reduces the maximum size to 500MiB, otherwise
the caches can become too big and get deleted by GitHub before they
can be used (the windows one was over 4GiB, and a new one
was created for every PR, quickly exceeding the 10 GB limit)
Dennis Brakhane
4acc10d3cc