tools: define xrange() in Python 3

__xrange()__ was removed in Python 3 in favor of __range()__.
This PR ensures similar functionality on both Python 2 and Python 3.

Discovered via https://travis-ci.com/nodejs/node/builds/79706150
(https://github.com/nodejs/node/pull/21942).

PR-URL: https://github.com/nodejs/node/pull/21945


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>