ROOT 6.22 Update, v33r1 branch (2020.07.28.)

These are changes going hand-in-hand with atlasexternals!710 (merged), to get our dev4LCG nightlies building again.

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/GITWebArea/nightlies/master--dev4LCG/

I'll also check after this whether the fixes are also needed in gaudi/Gaudi master. (I suspect they are...)

Ping @leggett, @simmons.