Externals Update, master branch (2021.07.02.)

Switched all projects to atlasexternals-2.0.110. The changes wrt. atlasexternals-2.0.109 are the following (atlasexternals@2.0.109...2.0.110):

• Made it possible to build ROOT with LLVM/Cling in Debug mode for dictionary debugging;
  • I did this while debugging ATLASG-1602, which I unfortunately still didn't manage to properly understand... 😦
• Removed the build of FastJet from all of the LCG based projects;
  • At the same time switched the build of FastJet in AnalysisBaseExternals to version 3.4.0, in sync with LCG_100_ATLAS_5;
  • Some details about the FastJet updates can be found on SPI-1929;
• Upgraded lwtnn to version 2.12 (for GCC 11 compatibility, see ATLINFR-4147);
• Upgraded prmon to version 2.2.1 (for GCC 11 compatibility, see ATLINFR-4147);
• Removed some unnecessary printouts from the build of dictionaries and converters.

At the same time upgraded all LCG based releases (with the exception of DetCommon of course) to LCG_100_ATLAS_5. To complete the migration to the new FastJet version.