test: add a test for gccgo bug #32901

This CL adds a test for gccgo bug #32901: not all the type
descriptors are registered and thus deduplicated with types
created by reflection. It needs a few levels of indirect imports
to trigger this bug.

Updates #32901.

Change-Id: Idbd89bedd63fea746769f2687f3f31c9767e5ec0
Reviewed-on: https://go-review.googlesource.com/c/go/+/184718Reviewed-by: Ian Lance Taylor <iant@golang.org>

test/fixedbugs/issue32901.dir/a.go

+// Copyright 2019 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 a
+
+type T struct { x int }
+
+func F() interface{} {
+	return [2]T{}
+}
+
+func P() interface{} {
+	return &[2]T{}
+}

test/fixedbugs/issue32901.dir/b.go

+// Copyright 2019 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 b
+
+import "./a"
+
+func F() interface{} {
+	return a.F()
+}
+
+func P() interface{} {
+	return a.P()
+}

test/fixedbugs/issue32901.dir/c.go

+// Copyright 2019 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 c
+
+import "./b"
+
+func F() interface{} {
+	go func(){}() // make it non-inlineable
+	return b.F()
+}
+
+func P() interface{} {
+	go func(){}() // make it non-inlineable
+	return b.P()
+}

test/fixedbugs/issue32901.dir/main.go

+// Copyright 2019 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 "./c"
+import "reflect"
+
+func main() {
+	x := c.F()
+	p := c.P()
+	t := reflect.PtrTo(reflect.TypeOf(x))
+	tp := reflect.TypeOf(p)
+	if t != tp {
+		panic("FAIL")
+	}
+}

test/fixedbugs/issue32901.go

+// rundir
+
+// Copyright 2019 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 32901: type descriptor equality bug in gccgo.
+
+package ignored