[bug#71672] bug#17811: RFE: build against multiple python stacks

Hi Pavel - back in 2014 (!), you suggested supporting python2 and python3
simultaneously: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=17811
Essentially by defining a new "python3" primary to sit alongside
"python".

Agreed that this is desirable in general. It's now being discussed in
  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=71672
via a somewhat different approach. I'd worry about making python3 a new
primary, since 3 vs. 2 is not the only distinction needed, as has been
discussed.

I'm closing this one to reduce duplication in the bugdb, but feel free
to reply on 71762 or open a new issue if desired. --thanks, karl.