test: add test case for CL 340609

The first version of CL 340609 for gofrontend passed all existing tests,
but not this one.

For #42076

Change-Id: I6491e2f186091bdae140b7f7befa511806a6478a
Reviewed-on: https://go-review.googlesource.com/c/go/+/340950


Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>