test: add test for gccgo issue #17640

Change-Id: Iec35f9b62982da40de400397bc456149216303dc
Reviewed-on: https://go-review.googlesource.com/32297Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue17640.go

+// run
+
+// Copyright 2016 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 main
+
+import "fmt"
+
+var results string
+
+type TwoInts struct {
+	x, y int
+}
+
+func f(x int) int { results = results + fmt.Sprintf("_%d", x); return x }
+
+func main() {
+	_ = [19]int{1: f(1), 0: f(0), 2: f(2), 6, 7}
+	_ = [2]int{1: f(4), 0: f(3)}
+	_ = TwoInts{y: f(6), x: f(5)}
+	_ = map[int]int{f(f(9) + 1): f(8), 0: f(7), f(22): -1}
+	if results != "_1_0_2_4_3_6_5_9_10_8_7_22" {
+		fmt.Printf("unexpected: %s\n", results)
+		panic("fail")
+	}
+}