test: add test for gccgo bug 23545

The fix is CL 91035.

Build only with gccgo at the moment, as it hits issue #23546.

Updates #23545.

Change-Id: I3a1367bb31b04773d31f71016f8fd7bd1855d7b5
Reviewed-on: https://go-review.googlesource.com/89735
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

test/fixedbugs/issue23545.go

@@ -0,0 +1,35 @@
+// run
+
+// Copyright 2018 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.
+
+// +build gccgo
+
+// Issue 23545: gccgo didn't lower array comparison to
+// proper equality function in some case.
+// TODO: build only on gccgo for now, as it hits issue
+// #23546.
+
+package main
+
+func main() {
+	if a := Get(); a != dummyID(1234) {
+		panic("FAIL")
+	}
+}
+
+func dummyID(x int) [Size]interface{} {
+	var out [Size]interface{}
+	out[0] = x
+	return out
+}
+
+const Size = 32
+
+type OutputID [Size]interface{}
+
+//go:noinline
+func Get() OutputID {
+	return dummyID(1234)
+}