Tag to be used with the 21.X branches of atlas/athena. Updates in this tag: - Updated the build of Davix to happen on any linux system that should be able to build it. (Changed from only building it on SLC6 and CC7.) - Updated the Geant4 version to 10.1.patch03.atlas07. - Updated the lwtnn version to 2.8. - Suppressed some warnings from new CMake versions.