We need to apply the same patch upstream in 2.5 tree so I have asked Paul why the flag was needed and if it can be removed. So it can be safely removed also upstream.
Update : patch applied both in trunk and firebird 2.5.x release branch.
gds_relay target was removed from darwin makefile comments (target was removed many years ago by Alex)
It should be removed from all makefiles in 2.5.x branch (seems to be removed in trunk)