Allow building from tarball without Python

[rockdaboot]

This adds the DAFSA files to the tarball, which allows building without installing python.
It allows, for example, to reduce the size of build container images.

[eli-schwartz]

I think that this is overall reasonable. However configure.ac still checks for python without overriding the second argument to the macro, which means that python is mandatory at configure time even if it is never run.

(Quick way to test this out: PYTHON=/bin/false ./configure. On this PR branch it errors out telling me that a mandatory python >=2.7 could not be detected.)

You will also want to make sure that when python isn't found, it ends up set to the "missing" tool or else check whether the distributed file is present and fail if not present -- this will handle cases where the user clones the repository and then runs autoreconf to build the configure script, but doesn't have python installed.

...

This change is probably not really necessary to implement in meson as well -- because meson's reference implementation is written in python. There's a c99 implementation of meson called "muon", and the meson.build files will still work with muon, but simply require python to also be installed, which may not be a big deal since people who really want to avoid installing python may want to avoid installing anything, and the configure script has zero dependencies other than POSIX required utilities + POSIX make, and that's usually considered pretty ideal in these "must avoid too many dependencies" scenarios.

So I don't know how much interest there is in teaching meson to use the pre-distributed BUILT_SOURCES. But if the interest exists, I can wire it up.

[rockdaboot]

However configure.ac still checks for python

Thx, good catch!
The applied changes to configure.ac work for me, but please also have another look.

So I don't know how much interest there is in teaching meson to use the pre-distributed BUILT_SOURCES. But if the interest exists, I can wire it up.

I don't want to stop you from wiring it up, but IMO you are right that we can just wait until requested.