After this commit the testsuite passes on mips64le.

Fixes golang/go#20340.

Change-Id: I6b3f673674af107fd6d249ccf5e695e0e50a41bb
Reviewed-on: https://go-review.googlesource.com/43430Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>