The ebuilds for xf4vnc use x86 binary tar.gz instead of compiling the source. This prevents it from even possibly working on non-x86 systems.
Adding xf4vnc's maintainer to CC, since this requires source releases of xf4vnc
FYI: Version 4.3.0.999 has been released. http://sourceforge.net/projects/xf4vnc
Created attachment 37678 [details] Ebuild for RealVNC 4.0 Binaries The ebuild described above
Sorry - Posted attachment to wrong bug
When upstream releases the source in tarballs or patches against existing xorg releases changeing to do a compilation would be possible.