The ebuild removes the openjpeg dir from the gs tar in an attempt to force the use of media-libs/openjpeg’s version of the library, but gs’s configure.ac is incapable of that; it only looks for the local version when the --enable-openjpeg configure flag is passed and disables openjpeg if that is not found. gs needs a configure.ac patch and an eautoreconf to have any chance of linking against the system libopenjpeg.so. 9.07 (which is out) uses --enable-openjpeg be default, but still only works as above.
Thanks! This is fixed in ghostscript-gpl-9.09 as we use the bundled openjpeg version again, see upstream bug report for details. The tracker for libraries bundled in ghostscript is #206893.