[dev.regabi] test: add a test for inlining closures

Add a test case for issue 43818. We don't want to mark as inlinable a
function with a closure that has an operation (such as OSELRECV2) that
we don't currently support for exporting. This test case fails to
compile without the fix for #43818.

Updates #43818

Change-Id: Ief322a14aefaefc6913c40a6b8505214bd622fda
Reviewed-on: https://go-review.googlesource.com/c/go/+/288392
Run-TryBot: Dan Scales <danscales@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>

test/closure7.go

@@ -0,0 +1,28 @@
+// run
+
+// Copyright 2020 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
+
+func g(f func()) {
+}
+
+// Must have exportable name
+func F() {
+	g(func() {
+		ch := make(chan int)
+		for {
+			select {
+			case <-ch:
+				return
+			default:
+			}
+		}
+	})
+}
+
+func main() {
+	F()
+}