http://archives.gentoo.org/gentoo-dev/msg_d3e2b252149a4130c31e3069d3e9086e.xml -if built_with_use --missing false =sys-devel/gcc-$(gcc-version)* openmp ; then +if has_version =sys-devel/gcc-$(gcc-version)*[openmp] ; then ...works for me. Please change it on your next version/revision bump. Thanks!
fixed in the latest version available in portage w/o revision bump. thanks for the patch. 30 Jan 2010; Markus Meier <maekke@gentoo.org> imagemagick-6.5.8.8.ebuild: replace built_with_use with has_version by Gordon Malm in bug #302145