cmd/go: remove $WORK paths in generated binaries         Fixes issue 3748.
cmd/go: remove $WORK paths in generated binaries
        Fixes issue 3748.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/6357064

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang