cmd/compile/internal/ssa: cleanup godocs

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>

src/cmd/compile/internal/ssa/gen/main.go

@@ -75,6 +75,7 @@ func genOp() {
 	w := new(bytes.Buffer)
 	fmt.Fprintf(w, "// autogenerated: do not edit!\n")
 	fmt.Fprintf(w, "// generated from gen/*Ops.go\n")
+	fmt.Fprintln(w)
 	fmt.Fprintln(w, "package ssa")
 
 	fmt.Fprintln(w, "import \"cmd/internal/obj/x86\"")

src/cmd/compile/internal/ssa/gen/rulegen.go

@@ -140,6 +140,7 @@ func genRules(arch arch) {
 	w := new(bytes.Buffer)
 	fmt.Fprintf(w, "// autogenerated from gen/%s.rules: do not edit!\n", arch.name)
 	fmt.Fprintln(w, "// generated with: cd gen; go run *.go")
+	fmt.Fprintln(w)
 	fmt.Fprintln(w, "package ssa")
 	if *genLog {
 		fmt.Fprintln(w, "import \"fmt\"")

src/cmd/compile/internal/ssa/opGen.go

 // autogenerated: do not edit!
 // generated from gen/*Ops.go
+
 package ssa
 
 import "cmd/internal/obj/x86"

src/cmd/compile/internal/ssa/rewriteAMD64.go

 // autogenerated from gen/AMD64.rules: do not edit!
 // generated with: cd gen; go run *.go
+
 package ssa
 
 import "math"

src/cmd/compile/internal/ssa/rewritegeneric.go

 // autogenerated from gen/generic.rules: do not edit!
 // generated with: cd gen; go run *.go
+
 package ssa
 
 import "math"