cmd/gc: mark OGOTO as a statement for formatters.

Nodes of goto statements were corrupted when written
to export data.

Fixes #7023.

R=rsc, dave, minux.ma
CC=golang-codereviews
https://golang.org/cl/46190043

src/cmd/gc/fmt.c

@@ -1039,6 +1039,7 @@ static int opprec[] = {
 	[OEMPTY] = -1,
 	[OFALL] = -1,
 	[OFOR] = -1,
+	[OGOTO] = -1,
 	[OIF] = -1,
 	[OLABEL] = -1,
 	[OPROC] = -1,

test/fixedbugs/issue7023.dir/a.go

+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+func Foo() {
+	goto bar
+bar:
+}

test/fixedbugs/issue7023.dir/b.go

+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package b
+
+import (
+	"./a"
+)
+
+var f = a.Foo

test/fixedbugs/issue7023.go

+// compiledir
+
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 7023: corrupted export data when an inlined function
+// contains a goto.
+
+package ignored