Since bash-completion 2.9, it was no longer possible to override
the completionsdir through prefix. [1] In 2.10, the overridability
was re-estabilished but this time through datadir variable. [2]
This should not really matter except for developers installing the project
into a custom prefix or distros using per-package prefixes like NixOS.
[1]: 81ba2c7e7d
[2]: https://github.com/scop/bash-completion/pull/344
This allows us to easily build just libfwupd in a flatpak manifest without
installing dozens of deps to build things we're just going to delete anyway.
This currently just outputs the current list of devices with releases and makes
it possible to integrate firmware version reporting with other tools like mgmt.
