Created attachment 4480 
quick-n-dirty libxfce4ui-4.10.0 patch

Can't compile libxfce4ui after making distclean. The error is:
main.c:33:29: fatal error: about-dialog-ui.h: No such file or directory

Turns out the file "about-dialog-ui.h" is being deleted by "make distclean", I traced this to "about-dialog-ui.h" being part of $xfce4_about_built_sources in xfce4-about/Makefile.in:
xfce4_about_built_sources = \
        about-dialog-ui.h

This bug is always reproductible on my built-from-scratch linux x86_64 using make-3.82.
I'm also attaching a simple patch, which seems to have fixed the error for me.