QSegfalutHandler disables core dumps for SEGV

QSegfaultHandler installs its own handler for SEGV, however this doesn't call the default handler, so core dumps can no longer be created. As QSegfaultHandler is initialized for gui apps using the eglfs platform (in qfbvthandler), this effectively means that core dumps can't be genereated for GUI apps.

A workaround can be to set QT_QPA_ENABLE_TERMINAL_KEYBOARD=1 if you don't have keyboard.