Xorg creates the log-dir in its output path because X crashes if it can't write
to its logfile. On a regular distro, this dir would be installed into the root
to prevent that from happening but with Nix, it sits in the read-only Nix store.
Ironically, when Xorg tries to write here, it fails and crashes.
To make Xorg log to /var/log, we have to stop the build script from trying to
create the log-dir as the sandbox doesn't (and shouldn't) have access to /var.
This creates a runtime dependency on /var when running as root but that should
exist on any Linux system (on NixOS, journald always creates /var/log).
Previously, the startx displayManager required some workarounds for logfiles
which are obsolete now.
patchPhase -> postPatch because overriding the patchPhase prevents patches from
being applied
