I started with a very base installation and base-devel
I am using xz for makepkg compression using the -T config for multithreading to beat zstd in speed and ofcourse size.
Looked at the list of pkgs so I started at the bottom, with xz

https://raw.githubusercontent.com/archlinux/svntogit-packages/packages/xz/trunk/PKGBUILD

The gpg signature in this pkg doesn't check out, and fails.
Using the newer pkg from AUR xz-git checks out fine.

I wonder how many packages Arch is pushing out as binaries that no-longer checkout and are therefor BAD, suspicious, not matching upstream?

I will keep reporting

Edit: Maybe due to a report about this in reddit/r/archlinux the key needed is again available and the package builds normally.

Edit2: Tried it again with the validated signature
message.c: In function ‘progress_speed.part.0’:
message.c:384:35: error: ‘%s’ directive output may be truncated writing up to 23 bytes into a region of size between 0 and 14 [-Werror=format-truncation=]
  384 |  snprintf(buf, sizeof(buf), "%.*f %s",
      |                                   ^~
In file included from /usr/include/stdio.h:866,
                 from private.h:23,
                 from message.c:13:
/usr/include/bits/stdio2.h:71:10: note: ‘__builtin___snprintf_chk’ output between 3 and 337 bytes into a destination of size 16
   71 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   72 |        __glibc_objsize (__s), __fmt,
      |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   73 |        __va_arg_pack ());
      |        ~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[3]: *** [Makefile:633: xz-message.o] Error 1
make[3]: Leaving directory '/src/xz/src/xz-5.2.5/src/xz'
make[2]: *** [Makefile:422: all-recursive] Error 1
make[2]: Leaving directory '/src/xz/src/xz-5.2.5/src'
make[1]: *** [Makefile:616: all-recursive] Error 1
make[1]: Leaving directory '/src/xz/src/xz-5.2.5'
make: *** [Makefile:483: all] Error 2
==> ERROR: A failure occurred in build().
    Aborting...
One of the things I realized while making this is that with Obarun you can have the base installed without s6/66 and libraries, it is a functional chroot. With arch doing the same, meaning the same list of base pkg - systemd, at least systemd-libs is drawn as a dependency, so it is always present for building.

This means that Obarun is more like the real Arch of the beginning than Arch is now. You can not build an arch package without systemd parts being present.
core/iputils

has a make dependency, no running dependency, with systemd, removing it from PKGBUILD it builds and produces the following three references to it:
Run-time dependency systemd found: NO (tried pkgconfig and cmake)

CONFIGURATION
Capatiblity (with libcap): true
IDN (with libidn2): true
I18N (with gettext): true
systemd: false

SYSTEM PATHS
prefix: /usr
bindir: /usr/bin
localedir: /usr/share/locale
sbindir: /usr/bin
systemdunitdir:
gettext

requires emacs and indirectly parts of udev, in obarun found in eudev instead of being part of systemd. The build dependency for emacs installation is satisfied through Obarun and emacs is installed and functional, but building gettext fails without the presence of systemd and libs.
else :; fi
emacs: error while loading shared libraries: libsystemd.so.0: cannot open shared object file: No such file or directory
make[4]: *** [Makefile:2172: start-po.elc] Error 127
make[4]: Leaving directory '/src/gettext/src/gettext-0.21/gettext-tools/emacs'
make[3]: *** [Makefile:2355: all-recursive] Error 1
make[3]: Leaving directory '/src/gettext/src/gettext-0.21/gettext-tools'
make[2]: *** [Makefile:2223: all] Error 2
make[2]: Leaving directory '/src/gettext/src/gettext-0.21/gettext-tools'
make[1]: *** [Makefile:403: all-recursive] Error 1
make[1]: Leaving directory '/src/gettext/src/gettext-0.21'
make: *** [Makefile:359: all] Error 2
more pkgs seem to have to be built away from the disease
fakeroot requires systemd to be built, using fakeroot-git PKGBUILD and removing systemd as build dependency runs into this error: (this is a package that comes from debian, so no surprise, but this is key in building pkgs in Arch).
libfakeroot.c: In function ‘statx’:
libfakeroot.c:102:50: error: ‘_STAT_VER’ undeclared (first use in this function)
  102 | # define INT_NEXT_FSTATAT(a,b,c,d) NEXT_FSTATAT64(_STAT_VER,a,b,c,d)
      |                                                  ^~~~~~~~~
fakerootconfig.h:15:53: note: in definition of macro ‘NEXT_FSTATAT64’
   15 | # define NEXT_FSTATAT64(a,b,c,d,e) next___fxstatat64(a,b,c,d,e)
      |                                                     ^
libfakeroot.c:2473:5: note: in expansion of macro ‘INT_NEXT_FSTATAT’
 2473 |   r=INT_NEXT_FSTATAT(dirfd, path, &st, flags);
      |     ^~~~~~~~~~~~~~~~
make[2]: *** [Makefile:668: libfakeroot.lo] Error 1
make[2]: *** Waiting for unfinished jobs....
mv -f .deps/communicate.Tpo .deps/communicate.Plo
mv -f .deps/faked.Tpo .deps/faked.Po
make[2]: Leaving directory '/src/fakeroot/src/fakeroot'
make[1]: *** [Makefile:690: all-recursive] Error 1
make[1]: Leaving directory '/src/fakeroot/src/fakeroot'
make: *** [Makefile:459: all] Error 2
==> ERROR: A failure occurred in build().
On the other hand, if you just remove the systemd from build dependencies on Arch's PKGBUILD and use Arch's patches the pkg builds without errors or warnings,

So why do they have systemd as a build dependency I don't understand
i don't say anything, but this thread is really interesting.

Please continue to make reports
coreutils fails on some tests:
tty.sh is the one failing, but this is the summary at the end:
PASS: tests/misc/tsort.pl
FAIL: tests/misc/tty.sh
PASS: tests/misc/usage_vs_getopt.sh
PASS: tests/misc/unexpand.pl

SKIP tests/factor/t36.sh (exit status: 77)

============================================================================
Testsuite summary for GNU coreutils 8.32
============================================================================
# TOTAL: 621
# PASS:  495
# SKIP:  125
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0
============================================================================
See ./tests/test-suite.log
Please report to bug-coreutils@ gnu.org
============================================================================
make[4]: *** [Makefile:13025: tests/test-suite.log] Error 1
make[4]: Leaving directory '/src/coreutils/src/coreutils-8.32'
make[3]: *** [Makefile:13133: check-TESTS] Error 2
make[3]: Leaving directory '/src/coreutils/src/coreutils-8.32'
make[2]: *** [Makefile:13388: check-am] Error 2
make[2]: Leaving directory '/src/coreutils/src/coreutils-8.32'
make[1]: *** [Makefile:12910: check-recursive] Error 1
make[1]: Leaving directory '/src/coreutils/src/coreutils-8.32'
make: *** [Makefile:13390: check] Error 2
==> ERROR: A failure occurred in check().
    Aborting...
EUREKA: ./src/coreutils-8.32/tests/misc/tty.sh

you have to be on a true tty to run this test successfully, not on a v-terminal, so once run from a true tty the test passes and the pkg is built.

Great learning experience people!
gcc-libs may be one to bypass while doing this, it took hours yesterday so I just left it running, at some point it filled up an 11GB partition and quit before finishing.
automake is a real disappointment, it is a key package required for building any package, and in addition to the minimal base-devel pkgs it brings in about 1GB of packages that must be present for it to build. It nearly resembles a desktop installation with all this installed, fonts, gtk, wayland, xorgproto, emacs, .... and again this substitution of eudev and libeudev instead of systemd, ...

At the end, because the Arch group of dependencies are not there and instead are Obarun satisfaction of dependencies, the building process fails due to tests failing. At least 3 in the two attempts I made. It also takes hours to build.

I should have maybe started alphabetically from a ... z instead of the other way around. If you can not build the minimal tools to build everything else without systemd ever being present ... then it makes no sense to make exceptions.

You can't build an Obarun installation from source without systemd being present. Indirectly systemd is present even when you can't see it. Even Microsoft's c compiler is mentioned in building automake.

The next step is how Hyperbola stands out to the test, claiming it is all free. How does huperbola following arch recipe builds the minimal tools needed to make packages?
Here comes another surprise, automake-git from AUR, although marked as 1.15 it builds the same 1.16.3 but doesn't include all those "checkdependencies" in the list. It builds fast and easy with minimal build dependencies.

So the saga continues. Should I go now back to where I started, with my built packages as base and rebuild what I've built?

Will automake fail building packages that involve dependencies of the failed checks?
guile failure:
PASS: test-smob-mark-race
wrote `/src/guile/src/guile-2.2.6/cache/guile/ccache/2.2-LE-8-3.A/src/guile/src/guile-2.2.6/test-suite/standalone/test-stack-overflow.go'
allocate_stack failed: Cannot allocate memory
allocate_stack failed: Cannot allocate memory
allocate_stack failed: Cannot allocate memory
allocate_stack failed: Cannot allocate memory
allocate_stack failed: Cannot allocate memory
PASS: test-stack-overflow
wrote `/src/guile/src/guile-2.2.6/cache/guile/ccache/2.2-LE-8-3.A/src/guile/src/guile-2.2.6/test-suite/standalone/test-out-of-memory.go'
GC Warning: Failed to expand heap by 134348800 bytes
GC Warning: Failed to expand heap by 134217728 bytes
GC Warning: Out of Memory! Heap size: 1 MiB. Returning NULL!
error creating finalization thread: Cannot allocate memory
GC Warning: Failed to expand heap by 1000132608 bytes
GC Warning: Failed to expand heap by 1000001536 bytes
GC Warning: Out of Memory! Heap size: 1 MiB. Returning NULL!
mmap(PROT_NONE) failed
FAIL: test-out-of-memory
==================================
1 of 39 tests failed
Please report to bug-guile@ gnu.org
==================================
make[5]: *** [Makefile:2661: check-TESTS] Error 1
make[5]: Leaving directory '/src/guile/src/guile-2.2.6/test-suite/standalone'
make[4]: *** [Makefile:2788: check-am] Error 2
make[4]: Leaving directory '/src/guile/src/guile-2.2.6/test-suite/standalone'
make[3]: *** [Makefile:2790: check] Error 2
make[3]: Leaving directory '/src/guile/src/guile-2.2.6/test-suite/standalone'
make[2]: *** [Makefile:1887: check-recursive] Error 1
make[2]: Leaving directory '/src/guile/src/guile-2.2.6/test-suite'
make[1]: *** [Makefile:1857: check-recursive] Error 1
make[1]: Leaving directory '/src/guile/src/guile-2.2.6'
make: *** [Makefile:2244: check] Error 2
==> ERROR: A failure occurred in check().
    Aborting...
a year later
I also failed to build some packages from AUR, particularly audacium. I had to use the EndeavourOS live cd to build a package in a clean chroot . I have had some problems with it too: in a clean chroot you can't install dependencies from AUR. So I had to build the dependencies in a live sd and install them into the chroot. Only then the package was built without problems. I had to mount a swap partition to build package in live cd.
eric wroteuse docker image and add repo to pacman from the docker itself. This can help you to understand how to do it: https://gitlab.com/geraldwuhoo/docker-aurutils
Thanks for the tip, but I was not impressed with my first attempts to use docker. Apparently I need to make another effort and understand it thoroughly.

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