system/verbatim-files: sysctl.d/99-sysctl.conf: chmod 644.
system/verbatim-files: xsession: move Xsession and session-shutdown back from lightdm-session/.
system/usr-files: add a new stage and install /usr/share/xsessions/custom.desktop.
system/verbatim-toplevel: ditch.
system/usr-files: lib/sysusers.d/makepkg.conf: install a sysusers.d definition for the 'build' group.
system/archlinux: ditch pacman.conf and makepkg.conf for different architectures.

Different architectures will come in different branches.
system/archlinux: makepkg.conf: sanitize a bit.