_vm_map_clip_end allocates memory M_WAITOK for !system_map vm_maps. Add
WITNESS warning annotation for !system_map callers who may be holding
The warning in vm_map_delete may be redundant, if the loop is always
entered. I don't know enough about these functions to say whether it is
redundant or not. vm_map_delete is the path through which we actually
encountered the warning.