If you're using a slightly older libX11 that doesn't have the x11-xcb stuff built in, you can't configure startup-notification. The tail of the output when building on NetBSD 5.0 using the pkgsrc buid framework: checking whether realloc (NULL,) will work... yes checking execinfo.h usability... no checking execinfo.h presence... no checking for execinfo.h... no checking pkg-config is at least version 0.9.0... yes checking for xcb... yes checking for xcb_aux... yes checking for xcb_event... yes checking for x11_xcb... no configure: error: Cannot find x11-xcb *** Error code 1 Stop. make: stopped in /usr/pkgsrc/x11/startup-notification *** Error code 1 Stop. This breaks (for me) devel/monotone-viz (via x11/lablgtk, x11/gnome-panel, and devel/libwnck), and some more packages. Some option to build without this bleeding-edge support "would be nice". I also reported this to the pkgsrc people; maybe they can find some workaround, but a real fix is of course better. See http://mail-index.netbsd.org/pkgsrc-users/2011/10/08/msg015143.html for any possible followup on that front (none so far).
x11-xcb is no longer very bleeding-edge.
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