Add a test by making misc/cgo/testshared/src/trivial.go marginally less
trivial.

Fixes #25970.

Change-Id: I8815d0c56b8850fcdbf9b45f8406f37bd21b6865
Reviewed-on: https://go-review.googlesource.com/120235
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>