Also invert it, which means it no longer needs to cross the cgo
package boundary.

Change-Id: I393cd073bda02b591a55d6bc6b8bb94970ea71cd
Reviewed-on: https://go-review.googlesource.com/8082Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>