Building gnome-system-monitor-2.28.1 on OS X 10.4:

g++ -DHAVE_CONFIG_H -I. -I.. -DPROCMAN_DATADIR=\""/sw/share/procman/"\" -DGNOMELOCALEDIR=\""/sw/share/locale"\" -DDATADIR=\""/sw/share"\" -I/sw/include/glib-2.0 -I/sw/lib/glib-2.0/include -I/sw/lib/fontconfig2/include -I/sw/include/gconf/2 -I/sw/include/libgtop-2.0 -I/sw/include/libwnck-1.0 -I/sw/include/gtk-2.0 -I/sw/lib/gtk-2.0/include -I/sw/include/atk-1.0 -I/sw/include/cairo -I/sw/include/pango-1.0 -I/sw/include/pixman-1 -I/sw/include/freetype2 -I/sw/include -I/sw/include/gtkmm-2.4 -I/sw/lib/gtkmm-2.4/include -I/sw/include/giomm-2.4 -I/sw/lib/giomm-2.4/include -I/sw/include/pangomm-1.4 -I/sw/lib/pangomm-1.4/include -I/sw/include/gtk-unix-print-2.0 -I/sw/include/atkmm-1.6 -I/sw/include/gdkmm-2.4 -I/sw/lib/gdkmm-2.4/include -I/sw/include/glibmm-2.4 -I/sw/lib/glibmm-2.4/include -I/sw/include/sigc++-2.0 -I/sw/lib/sigc++-2.0/include -I/sw/include/cairomm-1.0 -I/sw/include/libxml2 -I/sw/include/librsvg-2 -I/sw/include/dbus-1.0 -I/sw/lib/dbus-1.0/include -I/usr/X11R6/include -I/usr/X11/include  -I/sw/include  -Wall -std=c++98 -g -O2 -MT openfiles.o -MD -MP -MF .deps/openfiles.Tpo -c -o openfiles.o openfiles.cpp
openfiles.cpp: In function 'char* friendlier_hostname(const char*, int)':
openfiles.cpp:70: error: 'NI_IDN' was not declared in this scope
make[2]: *** [openfiles.o] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2

I think NI_IDN is a glibc extension, not part of the standard...whatever-function it's extending.