build: disable cgo on Windows/amd64
build: disable cgo on Windows/amd64

Apparently it is broken.  Disable so that dashboard
will let us see other breakages on Windows.

R=golang-dev, bradfitz
CC=golang-dev
http://codereview.appspot.com/5477081

pombredanne/go-deleteme,dsriram/golang,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,gnanderson/go,dsriram/golang,gnanderson/go,dsriram/golang,dsriram/golang,tv42/old-go,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,gnanderson/go,tv42/old-go,apparentlymart/golang,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go