[$] One more pidfdfs surprise

The "pidfdfs" virtual filesystem was added to the 6.9 kernel release as away to export better information about running processes to user space. Itreplaced a previous implementation in a way that was, on its surface, fullycompatible while adding a number of new capabilities. This transition,which was intended to be entirely invisible to existing applications,already ran into trouble in March, when amisunderstanding with SELinux caused systems with pidfdfs to fail to bootproperly. That problem was quickly fixed, but it turns out that there wasone more surprise in store, showing just how hard ABI compatibility can beat times.