Debian 7 ships Python 3.2 by default. That's too old for our
upcoming build requirement of Python 3.5.
This commit adds a Python 3.5 package for wheezy that backports
the Python 3.5 from a much later Debian version.
The patch was inspired by the existing patch for Python 2.7.
However, it needed additional work. The changes and reasons
should all be documented in the changelog file as part of the
package diff we apply.
I'm a bit disappointed we had to disable PGO. But it was
reliably segfaulting during the build. I didn't feel like going
down that rabbit hole.
MozReview-Commit-ID: ABpHW1KYFQP
2d042e7643