[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>