test: add new test that gccgo failed to compile

Updates #22305

Change-Id: I0e6bbd880599fc1b70d0378b746d162d4a846c65
Reviewed-on: https://go-review.googlesource.com/91556
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

test/fixedbugs/issue22305.go

+// compile
+
+// Copyright 2017 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 22305: gccgo failed to compile this file.
+
+package main
+
+var F func() [0]func()
+var i = 2
+var B = F()[i]
+
+func main() {}