I have using lxde-base/lxmenu-data and lxde-base/menu-cache for all versioned ebuilds (0.7.0) or whatever.. and for dev ebuilds I am using the lxqt-base/menu-cache-9999 etc. versions.
I suspect the nature of these two packages is going to change in the future upstream, I'm not sure what to do about them.. 

I can post a patch for gtk-doc on gentoo-bugs but i believe the patch is only relevant to 9999 and there is no dev ebuild in tree.. so I actually need both dev ebuilds added to the tree... that would be the best fix IMHO