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-vdt
to makedepends (root
needs it) - Set C++ standard to 17 since
abseil-cpp
dropped support of C++11 Makehepmc-docs
any
Edited by Eric Long