gdb: Add iteration wrapper for intrusive_set_external_comparator
gdb: Add iteration wrapper for intrusive_set_external_comparator

scylladb/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla