This will break the build with versions of clang that have support for
counted_by (as it has been reverted in main but reapplication to main is
being actively worked on) because while annotating pointers with this
attribute is a goal of the counted_by attribute, it is not ready yet.
Please consider removing this and adding a TODO to annotate it when
support is available.

It's really unpleasant that we keep getting new attributes that we
seemingly are encouraged to use and get sent patches for it. And then we
learn a little later that that stuff isn't ready yet. It's annoying. I
know it isn't your fault but it would be wise to be a little more
careful. IOW, unless both clang and gcc do support that thing
appropriately don't send patches to various subsystems for this.

In any case, this is now fixed. I pulled an updated version from David.