currently, our ccache configuration by default is less effective than it could be, as its caches are effectively invalidated on every (even snapshot on stable branch) update. we could probably get away with caching based on major version for the stable branches and the full version (_p included and all) for the development branches (gcc:14 right now). we should also make the cache key retrieval as fast as possible, and should try to avoid patching the compiler if possible. to do this, we could install a ${COMPILER}-cachekey file with a cat shebang that contains the major version of the compiler for release branches and the full ${PV} for the snapshot branches. while a bit ugly, this avoids hacking gcc/clang and just leaves us with a somewhat simple mechanism to adjust the key. wdyt?
