Hello Guix!

GNOME (actually ‘gnome-settings-daemon’) pops up a notification upon low
disk space that looks like this:

    Low Disk Space on “filesystem root”

    [ Empty Trash ]    [ Examine ]

The “Examine” button spawns the Disk Space Analyzer (aka Baobab) and the
“Empty Trash” button does its thing.

The untested patch below adds a ‘guix gc’ button, which is probably more
important than the other two on Guix System.

I’m not sure whether implementing it is as simple as this: is it OK to
block during GC or should it be done in a separate process?

If someone here has more insight or would like to give it a try, please
let me know!

Ludo’.