Otherwise, things like hp-setup segfault if you run them from another
nixpkgs checkout:
```
HP Linux Imaging and Printing System (ver. 3.20.5)
Printer/Fax Setup Utility ver. 9.0
Copyright (c) 2001-18 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.
[1] 4543 abort (core dumped) result/bin/hp-setup
```
907353b1e4