Same fix as golang.org/cl/15608 for package syscall.

Change-Id: I8de2369220e58140596325d7ea16c015aab90d1b
Reviewed-on: https://go-review.googlesource.com/15609
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>