test: add test for issue 18636

Updates #18636

Change-Id: I143c670c3940231e29f1814e0a03165682f53243
Reviewed-on: https://go-review.googlesource.com/43621Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

test/fixedbugs/issue18636.go

+// run
+
+// 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.
+
+package main
+
+import "runtime/debug"
+
+type Foo struct {
+	A [1 << 20]byte
+	B string
+}
+
+func run(c chan bool) {
+	f := new(Foo)
+	*f = Foo{B: "hello"}
+	c <- true
+}
+
+func main() {
+	debug.SetMaxStack(1 << 16)
+	c := make(chan bool)
+	go run(c)
+	<-c
+}