This CL only fixes the build, there are two failing tests:
RaceMapBigValAccess1 and RaceMapBigValAccess2
in runtime/race tests. I haven't investigated why yet.

Updates #9516.

Change-Id: If5bd2f0bee1ee45b1977990ab71e2917aada505f
Reviewed-on: https://go-review.googlesource.com/2401Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>