Building gnome-session-2.26.1 on OS X 10.4 fails:

gcc -DHAVE_CONFIG_H -I. -I.. -I../egg -Wall -Wmissing-prototypes -Wnested-externs -Wpointer-arith -Wno-sign-compare     -I/sw/lib/fontconfig2/include -I/sw/include/glib-2.0 -I/sw/lib/glib-2.0/include -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/libpng12 -I/sw/include/dbus-1.0 -I/sw/lib/dbus-1.0/include -I/sw/include/libglade-2.0 -I/sw/include/libxml2 -I/usr/X11R6/include -I/usr/X11/include -I/sw/include/gconf/2 -I/sw/include/orbit-2.0 -I/sw/include/dbus-1.0 -I/sw/lib/dbus-1.0/include -I/sw/include/glib-2.0 -I/sw/lib/glib-2.0/include -DORBIT2=1  -DLOCALE_DIR=\""/sw/share/locale"\" -DDATA_DIR=\""/sw/share/gnome-session"\" -DDBUS_LAUNCH=\"dbus-launch\" -DLIBEXECDIR=\"/sw/libexec\" -DGLADEDIR=\""/sw/share/gnome-session"\" -DGCONF_SANITY_CHECK=\""/sw/lib/gconf2/gconf-sanity-check-2"\" -DGCONFTOOL_CMD=\"/sw/bin/gconftool-2\"  -I/sw/include  -Os -c gs-idle-monitor.c
gs-idle-monitor.c: In function '_init_xtest':
gs-idle-monitor.c:294: error: 'XK_Alt_L' undeclared (first use in this function)
gs-idle-monitor.c:294: error: (Each undeclared identifier is reported only once
gs-idle-monitor.c:294: error: for each function it appears in.)
gs-idle-monitor.c:298: error: 'XK_Alt_R' undeclared (first use in this function)
make[3]: *** [gs-idle-monitor.o] Error 1

There's a missing #include for what defines the x11 keysyms