/usr/include/postgres-xc/server/gtm/ is in postgres-xc-server-dev 1.1-2ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/postgres-xc/server/gtm/assert.h
/usr/include/postgres-xc/server/gtm/elog.h
/usr/include/postgres-xc/server/gtm/gtm.h
/usr/include/postgres-xc/server/gtm/gtm_backup.h
/usr/include/postgres-xc/server/gtm/gtm_c.h
/usr/include/postgres-xc/server/gtm/gtm_client.h
/usr/include/postgres-xc/server/gtm/gtm_conn.h
/usr/include/postgres-xc/server/gtm/gtm_ext.h
/usr/include/postgres-xc/server/gtm/gtm_ip.h
/usr/include/postgres-xc/server/gtm/gtm_list.h
/usr/include/postgres-xc/server/gtm/gtm_lock.h
/usr/include/postgres-xc/server/gtm/gtm_msg.h
/usr/include/postgres-xc/server/gtm/gtm_opt.h
/usr/include/postgres-xc/server/gtm/gtm_opt_tables.h
/usr/include/postgres-xc/server/gtm/gtm_proxy.h
/usr/include/postgres-xc/server/gtm/gtm_seq.h
/usr/include/postgres-xc/server/gtm/gtm_serialize.h
/usr/include/postgres-xc/server/gtm/gtm_serialize_debug.h
/usr/include/postgres-xc/server/gtm/gtm_standby.h
/usr/include/postgres-xc/server/gtm/gtm_time.h
/usr/include/postgres-xc/server/gtm/gtm_txn.h
/usr/include/postgres-xc/server/gtm/gtm_utils.h
/usr/include/postgres-xc/server/gtm/ip.h
/usr/include/postgres-xc/server/gtm/libpq-be.h
/usr/include/postgres-xc/server/gtm/libpq-fe.h
/usr/include/postgres-xc/server/gtm/libpq-int.h
/usr/include/postgres-xc/server/gtm/libpq.h
/usr/include/postgres-xc/server/gtm/memnodes.h
/usr/include/postgres-xc/server/gtm/memutils.h
/usr/include/postgres-xc/server/gtm/palloc.h
/usr/include/postgres-xc/server/gtm/path.h
/usr/include/postgres-xc/server/gtm/pqcomm.h
/usr/include/postgres-xc/server/gtm/pqexpbuffer.h
/usr/include/postgres-xc/server/gtm/pqformat.h
/usr/include/postgres-xc/server/gtm/pqsignal.h
/usr/include/postgres-xc/server/gtm/proxy_utils.h
/usr/include/postgres-xc/server/gtm/register.h
/usr/include/postgres-xc/server/gtm/replication.h
/usr/include/postgres-xc/server/gtm/standby_utils.h
/usr/include/postgres-xc/server/gtm/stringinfo.h