libxfce4ui compile error

make[1]: Entering directory `/home/jd/xfce/libxfce4ui/xfce4-about'
  CC     xfce4_about-main.o
main.c: In function ‘main’:
main.c:472:46: error: ‘xfce_about_dialog_ui’ undeclared (first use in this function)
main.c:472:46: note: each undeclared identifier is reported only once for each function it appears in
main.c:473:37: error: ‘xfce_about_dialog_ui_length’ undeclared (first use in this function)
make[1]: *** [xfce4_about-main.o] Error 1
make[1]: Leaving directory `/home/jd/xfce/libxfce4ui/xfce4-about'
make: *** [all] Error 2