The current version of oracle-instantclient-basic has a file requirement won't match any version that can be download from the oracle website (or anywhere else). Here's an updated ebuild for it, probably needs a quick look over to be definite it's right, but it works for me.
Created attachment 92393 [details] ebuild ebuild
oracle-instantclient-{baisc,jdbc,sqlplus} updated. Thanks for reporting!