Tag to be used with the 21.X branches of atlas/athena. Main updates in this tag: - Fixed the build of HepMCAnalysis after the changes that were made in FastJet in the previous tag; - Minor changes to the Simage build; - Added the Findxz.cmake module, interesting mainly for the VP1 developers; - Updated to fjcontrib-1.033; - Updated FastJet and FastJetContrib to build correctly with the latest version of clang, now used on MacOS; - Added ACTS as a package. Not building it as part of any project though.