libgdk still needs xkb to be present to build successfully:

./configure [...] --enable-xkb=no
[...]
make[4]: Entering directory `/usr/local/src/gnome/gtk+/gtk'
/bin/sh ../libtool --tag=CC   --mode=link gcc -std=gnu99  -DGDK_PIXBUF_DISABLE_DEPRECATED -g -O2 -Wall   -o gtk-query-immodules-3.0 queryimmodules.o libgtk-x11-3.0.la ../gdk-pixbuf/libgdk_pixbuf-3.0.la ../gdk/libgdk-x11-3.0.la -pthread -L/usr/local/lib -lpangocairo-1.0 -lX11 -lXcomposite -lXdamage -lXfixes -latk-1.0 -lcairo -lgio-2.0 -lpangoft2-1.0 -lpango-1.0 -lfreetype -lfontconfig -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lrt -lglib-2.0 -lm
libtool: link: gcc -std=gnu99 -DGDK_PIXBUF_DISABLE_DEPRECATED -g -O2 -Wall -o .libs/gtk-query-immodules-3.0 queryimmodules.o -pthread  ./.libs/libgtk-x11-3.0.so -L/usr/local/lib /usr/local/src/gnome/gtk+/gdk/.libs/libgdk-x11-3.0.so ../gdk-pixbuf/.libs/libgdk_pixbuf-3.0.so ../gdk/.libs/libgdk-x11-3.0.so /usr/local/lib/libXinerama.so /usr/local/lib/libXrandr.so /usr/local/lib/libXcursor.so /usr/local/src/gnome/gtk+/gdk-pixbuf/.libs/libgdk_pixbuf-3.0.so /usr/local/lib/libpangocairo-1.0.so /usr/local/lib/libxml2.so /usr/local/lib/libxcb-render-util.so /usr/local/lib/libxcb-render.so /usr/local/lib/libXcomposite.so /usr/local/lib/libXext.so /usr/local/lib/libXdamage.so /usr/local/lib/libXfixes.so /usr/local/lib/libatk-1.0.so /usr/local/lib/libcairo.so /usr/local/lib/libpixman-1.so /usr/local/lib/libpng14.so /usr/local/lib/libXrender.so /usr/local/lib/libX11.so /usr/local/lib/libxcb.so /usr/local/lib/libXau.so /usr/local/lib/libXdmcp.so /usr/local/lib/libgio-2.0.so -lresolv /usr/local/lib/libpangoft2-1.0.so /usr/local/lib/libpango-1.0.so /usr/local/lib/libfontconfig.so /usr/local/lib/libfreetype.so -lz /usr/local/lib/libexpat.so /usr/local/lib/libgobject-2.0.so /usr/local/lib/libgmodule-2.0.so -ldl /usr/local/lib/libgthread-2.0.so -lpthread -lrt /usr/local/lib/libglib-2.0.so -lm -pthread
gtk+/gdk/.libs/libgdk-x11-3.0.so: undefined reference to `XkbBell'

When xkb is enabled in the library that provides it, the error disappears and the build completes without fail or (the way it looks here) it needs to be present to not be enabled....