cmd/ld: if we fail from an unexpected PE flags value, print it
cmd/ld: if we fail from an unexpected PE flags value, print it

R=golang-dev, minux.ma, r
CC=golang-dev
https://codereview.appspot.com/8709043

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