Add gcc12 definition for el9 (as well as centos9)
in LCG dev3/4 slots and in the upcoming LCG 103a SFT uses actual el9 builds instead of centos9, so I have to duplicate the legacy centos9-gcc12 definition as el9-gcc12.
in LCG dev3/4 slots and in the upcoming LCG 103a SFT uses actual el9 builds instead of centos9, so I have to duplicate the legacy centos9-gcc12 definition as el9-gcc12.