EvtGen build system has been migrated to CMake, including export of
config and targets files, making it much simpler to find and build
against. Utilise this here but allow fallback to previous behaviour in
case of using EvtGen versions built under previous system.
EvtGen build system has been migrated to CMake, including export of config and targets files, making it much simpler to find and build against. Utilise this here but allow fallback to previous behaviour in case of using EvtGen versions built under previous system.