Yeah, leave it as-is. `:libltdl` gets converted to a libtool dep under the hood, but this information is then lost and that is what trips up audit.

If you want you can add graphicsmagick to the list in this line: https://github.com/mxcl/homebrew/blob/0abaf95f714d295371285ac73f3be0843899706c/Library/Homebrew/cmd/audit.rb#L156

That's what I've been doing until I figure out the best way to actually fix it.