Add a blank line before the "package ssa" lines so the "autogenerated
don't edit" comments don't end up in godoc output.

Change-Id: I82bf90d52d426ce1a8e21483fc8f47b3689259c7
Reviewed-on: https://go-review.googlesource.com/20086Reviewed-by: Keith Randall <khr@golang.org>