Tag to be used with the 21.X branches of atlas/athena. Update(s) in this tag: - Made FindCairo.cmake work with >=LCG_92; - Stopped the (standalone) HDF5 build from installing PkgConfig files; - Switched the yampl build to downloading the source as a tarball instead of getting it from GitHub; - Added FindApfel.cmake to AtlasLCG.