Fix several packaging issues
- License: GPL3 -> LGPL-3.0-or-later (according to https://gitlab.cern.ch/hepmc/HepMC3/-/blob/3.2.6/COPYING)
- Add
cern-vdtto makedepends (rootneeds it) - Set C++ standard to 17 since
abseil-cppdropped support of C++11 Makehepmc-docsany
Edited by Eric Long