Created attachment 206902 [details]
According to make check-old, /usr/lib/debug/boot needs to be deleted, but make delete-old (and make delete-old-libs) fails to delete it as it is not empty: it contains two empty directories called "kernel" and "modules".
This might be related to the fact that I set WITHOUT_DEBUG_FILES=yes. I attach the full src.conf for more information.
This happens on 12-STABLE r321479, but it happened on earlier revisions too (I had not the time to report it before: I think it began this month).