Manual commit as the previous commit broke some Makefile logic.

Has been a to do item for time. These are independent from but used
by the bytecode trigger.

This reverts commit c17ddfbf66e2801ec620d49979aca3d7077d7002.

This causes breakage on several ports, and the next iteration
requires a full exp-run. See:

Differential Revision: https://reviews.freebsd.org/D34739

It was recently fixed and will be available in 13.2-RELEASE.
Since LTO is not enabled by default, it's ok to make it available.

Facilitates compiling, writing and removing bytecode files (.pyc)
in site-packages after all pkg transactions have been completed.

Technical details: https://wiki.freebsd.org/Python/CompiledPackages

Fixes reports of Python port builds as root failing on filesystem
violations due to bytecode file writes where the port did not include
them in the package.

For those ports/packages that currently package bytecode, some
checksum mismatches on those files may occur. This is harmless and
will be rectified, in large as part of a USE_PYTHON=distutils
overhaul to reduce churn.

While here, implement a long-standing todo item of letting lang/python
ports use python.mk bits. Not only does this obviate duplicate
variables in each Makefile, but SUB_LIST (also added) is used for
these triggers.

Co-authored by: tcberner
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D34739

* Python 3.7 will reach its End-of-Life on 2023-06-27.  Deprecate it and
  set the expiration date accordingly.

Approved by:	kai (python, maintainer)
Differential Revision:	https://reviews.freebsd.org/D37587

PR:		267648
Reported by:	glebius@
Exp-run by:	antoine@