The Python 3.8.x upgrade in #27754 needs more work.

On this ticket, we update to the latest 3.7.x release, which is 3.7.8 as of 2020-07-23. It was released 2020-06-27. It has lots of bug fixes and build fixes.

https://docs.python.org/release/3.7.8/whatsnew/changelog.html#changelog

Tarball: see checksums.ini

Previous and next Python upgrades:

• Upgrade to Python 3.7.x #25680 - Python 3.7.3
• Upgrade: Python 3.8.5 #27754 - Python 3.8.x
• Support Python 3.9 #30184 - Python 3.9.x

CC: @slel @dimpase @jhpalmieri @antonio-rojas @kiwifb

Component: packages: standard

Branch/Commit: u/mkoeppe/upgrade_python_to_3_7_8 @ 29d71d2

Issue created by migration from https://trac.sagemath.org/ticket/30210