Since the move to the new hooking mechanisms, we got remnant files after package upgrade.
They aren't part of the package and get generated by the depmod hook.
This addresses the issue by checking for tkg kernels module dirs and removing the ones missing a vmlinuz file (which is part of the package).
Due to the way it works, it'll also get rid of all past remnants to stay transparent for users.
In addition, disable `CONFIG_GCC_PLUGINS` when ccache is used as it's disruptive, and tweak ccache sloppiness with safe values.
Those changes combined are giving us near 100% cache hit rate on hot cache.
