appstreamcli required to generate appdata on GNOME flatpak SDK
gThumb requires appstreamcli
to generate the appdata file, file that should be part of the tarball but isn't.
That mean it can't be built on the GNOME flatpak SDK as appstreamcli
isn't found.
The appdata file should be generated when making a tarball instead.
Edited by Hubert Figuière