Followed the same test pattern in misc/cgo/testcarchive.

Change-Id: I2f863b5c24a28f0b38b0128ed3e8a92c17fb5b9f
Reviewed-on: https://go-review.googlesource.com/8985Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>