The extra fontforge cidmaps are required for fonts with a lot of characters (see link). Setting the USE flag cidmaps installs them.
Created attachment 84385 [details, diff] Diff to add cidmaps USE flag
Adding a local USE flag for cidmaps seems like a bad idea since it's a run-time issue, not a compile-time decision. Considering the size of fontforge installed, it's not unreasonable to simply install the extra cidmaps unconditionally. Added to fontforge-20060703-r1, thanks