The full list of changes wrt. 2.0.20 is technically a lot (atlasexternals@2.0.20...2.0.21), though conceptually it's a relatively short list.
Introduced fixes for AnalysisBaseExternals on Ubuntu and macOS. This was cherry picked from 1.0, where I'm trying to revive the analysis release builds for these platforms.
Added FindCURL.cmake to AtlasLCG to be able to use CURL from the LCG releases if necessary. This I made for ATLINFR-2820 originally, but in the end !20440 (merged) did make this update unnecessary. Still, it's not a bad update per se.
Updated the code handling Doxygen to work successfully with LCG_94. This is to address ATLINFR-2883.
Added a lot of CMake changes to make the code work smoothly with CMake >=3.13. (atlasexternals!418 (merged))
It's the last point which is truly non-trivial. I made a lot of changes in the central code to resolve some long standing issues. This required changing a variable naming convention (telling FindFoo.cmake where to look for Foo using FOO_ROOT) that I used in that code since the very beginning. This also means that to incorporate this update in the externals, I also had to update a number of files in this repository. These changes are in all cases very trivial. Though quite numerous...
I've been testing these changes for about a week now, still, since they are significant, it's not impossible that I may have missed something. Let's see what the CI tells us...
