MarsSeed [1] filed a deletion request for lib32-xcb-util-wm [2]: lib32-qt5* pkgs were the last consumers of this legacy lib32 build, and they have been deleted from AUR after 2015.
Therefore this library is useless to keep. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/lib32-xcb-util-wm/
