It doesn't work there ("out of memory") and doesn't really matter.
Fixes build (now that we enable cgo on the darwin/386 builder.)

Change-Id: I1d91e51ecb88c54eae39ac9a76f2c0b4e45263b0
Reviewed-on: https://go-review.googlesource.com/19004
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>