I think It's time to move on u.u
pacman -R gimp (2.8)
flatpak install https://flathub.org/repo/appstream/org.gimp.GIMP.flatpakref (2.10)
really.. Gimp is no longer the same from this update ^^
now It has a more professional look and smells a little bit like photoshop =]
https://www.gimp.org/release-notes/gimp-2.10.html
The strange thing is that the arch repo is SO OUTDATED on this packet.. anybody knows why? Maybe because of the flatpak adoption? the source code is still available, uhm...