Reported by Vagrant Cascadian <vagrant@debian.org>.

* Makefile.am (AUX_FILES): Add 'sanity-check-next.py'.

This is a followup to fdafd404325413da4d5fdd717c84e57a51c60fe2.  This
effect would to set 'GUIX_DISPLAYED_VERSION' to the empty string.

* Makefile.am (release): Remove '/v' from sed script for
GUIX_DISPLAYED_VERSION.

This works around <https://issues.guix.gnu.org/59717>, whereby heap
usage would go beyond what's reasonable, preventing compilation of the
'guix' package on armhf-linux.

This is a followup to ef82ba9dd94369926eb13325d5e7da4306d23dd7.

* Makefile.am (MODULES_PACKAGES1, MODULES_PACKAGES): New variables.
(MODULES_PACKAGES): Define in terms of them and use :=.
(MODULES_CORE, MODULES_SYSTEM, MODULES_CLI, MODULES_PO): Define with :=.

* Makefile.am (EXTRA_DIST): Sort.

* gnu/packages/linux.scm (linux-libre-5.19-version,
linux-libre-5.19-gnu-revision, deblob-scripts-5.19,
linux-libre-5.19-pristine-source, linux-libre-5.19-source,
linux-libre-headers-5.19, linux-libre-5.19): Remove variables.
* gnu/packages/aux-files/linux-libre/5.19-arm.conf,
gnu/packages/aux-files/linux-libre/5.19-arm64.conf,
gnu/packages/aux-files/linux-libre/5.19-i686.conf,
gnu/packages/aux-files/linux-libre/5.19-x86_64.conf: Delete files.
* Makefile.am (AUX_FILES): Remove them.

* gnu/packages/linux.scm (linux-libre-6.0-version,
linux-libre-6.0-pristine-source, linux-libre-6.0-source,
linux-libre-headers-6.0, linux-libre-6.0): New variables.
* gnu/packages/aux-files/linux-libre/6.0-arm.conf,
gnu/packages/aux-files/linux-libre/6.0-arm64.conf,
gnu/packages/aux-files/linux-libre/6.0-i686.conf,
gnu/packages/aux-files/linux-libre/6.0-x86_64.conf: New files.
* Makefile.am (AUX_FILES): Add them.

This is an experimental build system based on python-build-system
that implements PEP 517-compliant builds.

* doc/guix.texi (Build Systems): Add pyproject-build-system section.
* doc/contributing.texi (Python Modules): Mention pyproject.toml and the
PYTHON-TOOLCHAIN package, as well as differences to python-build-system.
* guix/build-system/pyproject.scm,
guix/build/pyproject-build-system.scm,
gnu/packages/aux-files/python/sanity-check-next.py,
gnu/packages/python-commencement.scm: New files.
* Makefile.am (MODULES): Register the new build systems.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add python-commencement.scm.
* gnu/packages/python.scm (python-sans-pip, python-sans-pip-wrapper): New
variables.

Co-authored-by: Marius Bakke <marius@gnu.org>

* gnu/packages/linux.scm (linux-libre-5.18-version,
linux-libre-5.18-gnu-revision, deblob-scripts-5.18,
linux-libre-5.18-pristine-source, linux-libre-5.18-source,
linux-libre-headers-5.18, linux-libre-5.18): Remove variables.
* gnu/packages/aux-files/linux-libre/5.18-arm.conf,
gnu/packages/aux-files/linux-libre/5.18-arm64.conf,
gnu/packages/aux-files/linux-libre/5.18-i686.conf,
gnu/packages/aux-files/linux-libre/5.18-x86_64.conf: Delete files.
* Makefile.am (AUX_FILES): Remove them.

* gnu/packages/linux.scm (linux-libre-5.19-version,
linux-libre-5.19-gnu-revision, deblob-scripts-5.19,
linux-libre-5.19-pristine-source, linux-libre-5.19-source,
linux-libre-headers-5.19, linux-libre-5.19): New variables.
* gnu/packages/aux-files/linux-libre/5.19-arm.conf,
gnu/packages/aux-files/linux-libre/5.19-arm64.conf,
gnu/packages/aux-files/linux-libre/5.19-i686.conf,
gnu/packages/aux-files/linux-libre/5.19-x86_64.conf: New files.
* Makefile.am (AUX_FILES): Add them.

* gnu/services/lightdm.scm: New service.
* tests/services/lightdm.scm: Test it.
* doc/guix.texi (X Window): Document it.
* gnu/local.mk (GNU_SYSTEM_MODULES): Register it.

Co-authored-by: L p R n d n <guix@lprndn.info>
Co-authored-by: Ricardo Wurmus <rekado@elephly.net>