Should fix Android builders on Darwin hosts.

Change-Id: I1554849bdf2ad2440529af7f93566fa6f11d5407
Reviewed-on: https://go-review.googlesource.com/c/164697
Run-TryBot: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>