It would be the same as `pacman -Ss base` plus `pacman -Ss base-devel`. Note "-Ssq" would probably be much more useful in this context.
I have no idea how yaourt (fails to) work(s), but FWIW the pacman command you used could be simplified - both the command and the processing needed would be reduced:pacman -Qim | grep -E "Name : xf".+devel
error: failed retrieving file 'archlinuxfr.db' from repo.archlinux.fr ...This suggests that you've been using yaourt - which is fine if you know what it is doing. But the resulting errors and looking for the depencies with pacman suggests that you don't know what it is doing. Use yaourt with caution (if at all).As already indicated above you need to update your aur