As the topic says, the xvid-1.1.0-r3 contains text relocations, which are fine with the current stable ffmpeg, but are not with the current ~arch'ed ffmpeg. Logs are following.
Created attachment 104742 [details] media-libs/xvid-1.1.0-r3 emerge log
Created attachment 104743 [details] scanelf-textrel.log
Yes. And the patch totally borked the thing so it got removed. *** This bug has been marked as a duplicate of 135326 ***