The part in gdkwindow-x11.c which uses XIEvent and friends is "protected"
by HAVE_XGENERICEVENTS, i.e., XGetEventData() has been found. (Xlib.h)
XIEvent and friends are defined in <X11/extension/XInput2.h> which is
included by gdkdisplay-x11.h if XINPUT_2 is defined.
The patch makes sure XIEvent is only used if XINPUT_2 is defined.
https://bugzilla.gnome.org/show_bug.cgi?id=667534