I would like to use BenchmarkRunningGoProgram to measure
changes for issue #15588. So the program in the benchmark
should import "os" package.

It is also reasonable that basic Go program includes
"os" package.

For #15588.

Change-Id: Ida6712eab22c2e79fbe91b6fdd492eaf31756852
Reviewed-on: https://go-review.googlesource.com/37914
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>