D7258: makefile: use Python 3 by default (BC)

[indygreg (Gregory Szorc)]

indygreg added a comment.


  This is ready for re-review. Please take a look @durin42.

REPOSITORY
  rHG Mercurial

BRANCH
  default

CHANGES SINCE LAST ACTION
  https://phab.mercurial-scm.org/D7258/new/

REVISION DETAIL
  https://phab.mercurial-scm.org/D7258

To: indygreg, #hg-reviewers, martinvonz
Cc: yuja, mharbison72, durin42, dlax, martinvonz, mercurial-devel