test: add test that gccgo failed to compile

Change-Id: I9ea6d4d8a9c1c63de36f2f3871dd5ac9201c0aac
Reviewed-on: https://go-review.googlesource.com/7523Reviewed-by: Minux Ma <minux@golang.org>

test/fixedbugs/bug495.go

+// compile
+
+// Copyright 2015 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.
+
+// Gccgo used to give an incorrect error
+// bug495.go:16:2: error: missing statement after label
+
+package p
+
+func F(i int) {
+	switch i {
+	case 0:
+		goto lab
+	lab:
+		fallthrough
+	case 1:
+	}
+}