test: add test case miscompiled by gccgo

R=golang-dev, bradfitz, rsc, iant
CC=golang-dev
https://golang.org/cl/7240043

test/fixedbugs/bug473.go

+// run
+
+// Copyright 2013 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.
+
+// Used to be miscompiled by gccgo, due to a bug in handling
+// initialization ordering.
+
+package main
+
+func F(a ...interface{}) interface{} {
+	s := 0
+	for _, v := range a {
+		s += v.(int)
+	}
+	return s
+}
+
+var V1 = F(V10, V4, V3, V11)
+
+var V2 = F(V1)
+
+var V3 = F(1)
+
+var V4 = F(2)
+
+var V5 = F(3)
+
+var V6 = F(4)
+
+var V7 = F(5)
+
+var V8 = F(V14, V7, V3, V6, V5)
+
+var V9 = F(V4, F(V12))
+
+var V10 = F(V4, V9)
+
+var V11 = F(6)
+
+var V12 = F(V5, V3, V8)
+
+var V13 = F(7)
+
+var V14 = F(8)
+
+func expect(name string, a interface{}, b int) {
+	if a.(int) != b {
+		panic(name)
+	}
+}
+
+func main() {
+	expect("V1", V1, 38)
+	expect("V2", V2, 38)
+	expect("V3", V3, 1)
+	expect("V4", V4, 2)
+	expect("V5", V5, 3)
+	expect("V6", V6, 4)
+	expect("V7", V7, 5)
+	expect("V8", V8, 21)
+	expect("V9", V9, 27)
+	expect("V10", V10, 29)
+	expect("V11", V11, 6)
+	expect("V12", V12, 25)
+	expect("V13", V13, 7)
+	expect("V14", V14, 8)
+}