Analysis HepMC CMake Update, master branch (2021.12.01.)
Now that HepMC (or hepmc3) is used through AtlasHepMCLib, TruthUtils and MCTruthClassifier should no longer make decisions based on whether HepMC is available or not. As it would have to replicate the logic of AtlasHepMC to do this correctly.
Instead, the decision whether or not to link against AtlasHepMCLib is now made purely based on XAOD_STANDALONE. Since it's only AnalysisBase that does not come with AtlasHepMC.
At the same time removed the optional usage of HEPUtils and MCUtils in TruthUtils. Since both of those are always available, in all of the projects that we build. So it's an error if either of them is not found.
This is all to fix ATLASG-1616.
P.S. The usage of TruthUtilsEnvironmentConfig.cmake should be made a little nicer as well. But that will need some update in the AtlasLCG code, so let's leave that for a future MR.