So the libpciaccess library seems to load pci.ids or pci.ids.gz, which _were_ provided by pciutils and now are provided by hwids. I'd suggest you should depend on sys-apps/hwids so that it is actually installed. hwids installs both the gzipped and the uncompressed file — so it's going to be your call whether you want to keep the zlib USE flag around I suppose.
Hellooo?
>=pciutils-3.1.9-r2 RDEPENDS on hwids, and <pciutils-3.1.9-r2 install pci.ids. Oh, wait. libpciaccess isn't even depending on pciutils. :\ Fixed, thanks!