/usr/include/pqxx/internal/gates/ is in libpqxx-dev 4.0.1+dfsg-3ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/pqxx/internal/gates/connection-dbtransaction.hxx
/usr/include/pqxx/internal/gates/connection-errorhandler.hxx
/usr/include/pqxx/internal/gates/connection-largeobject.hxx
/usr/include/pqxx/internal/gates/connection-notification_receiver.hxx
/usr/include/pqxx/internal/gates/connection-parameterized_invocation.hxx
/usr/include/pqxx/internal/gates/connection-pipeline.hxx
/usr/include/pqxx/internal/gates/connection-prepare-invocation.hxx
/usr/include/pqxx/internal/gates/connection-reactivation_avoidance_exemption.hxx
/usr/include/pqxx/internal/gates/connection-sql_cursor.hxx
/usr/include/pqxx/internal/gates/connection-transaction.hxx
/usr/include/pqxx/internal/gates/errorhandler-connection.hxx
/usr/include/pqxx/internal/gates/icursor_iterator-icursorstream.hxx
/usr/include/pqxx/internal/gates/icursorstream-icursor_iterator.hxx
/usr/include/pqxx/internal/gates/result-connection.hxx
/usr/include/pqxx/internal/gates/result-creation.hxx
/usr/include/pqxx/internal/gates/result-sql_cursor.hxx
/usr/include/pqxx/internal/gates/transaction-subtransaction.hxx
/usr/include/pqxx/internal/gates/transaction-tablereader.hxx
/usr/include/pqxx/internal/gates/transaction-tablewriter.hxx
/usr/include/pqxx/internal/gates/transaction-transactionfocus.hxx