fix windows/amd64 build with newest mingw-w64
fix windows/amd64 build with newest mingw-w64

R=alex.brainman, golang-dev
CC=golang-dev
http://codereview.appspot.com/4968048

Committer: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>

wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang