test: add test that failed with gccgo

Updates #33739

Change-Id: Ib7ce4bc51972fe49998f37f6e27baa6a2a036d5e
Reviewed-on: https://go-review.googlesource.com/c/go/+/191001Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue33739.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
+
+func F() func() {
+	return f
+}
+
+func f() {}

test/fixedbugs/issue33739.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 main
+
+import "a"
+
+func main() {
+	a.F()()
+}

test/fixedbugs/issue33739.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 33739: gccgo undefined symbol with cross-package inlining
+
+package ignored