Snort 2.0.5-r2 and 2.0.6 was marked ~amd64, but underlaying libraries (dev-libs/libprelude in this case) was not marked ~amd64. I had to do "repoman -I <stuff>" to commit the changes that bug 43990 required. Please test dev-libs/libprelude on the amd64 platform and give it the appropiate keywords.
Already added by avenj.