JonnyRobbie [1] filed a orphan request for xf86-input-wacom-git [2]:

There is a build error which has been present more then half a year, comments suggested working fix and the pkgbuild is still not updated.

[1] https://aur.archlinux.org/account/JonnyRobbie/ [2] https://aur.archlinux.org/pkgbase/xf86-input-wacom-git/