Cross Compiling undefined: ui errors

My example is working well on Fedora , but if I try to create a Windows Cross Compiling version from linux I got this errors.
I used go version 1.10.1 linux/amd64
Why ?
```
[mythcat@desk ~]$ GOOS=windows GOARCH=amd64 go build -o hello.exe go/src/gui_test/main.go
# command-line-arguments
go/src/gui_test/main.go:8:9: undefined: ui.Main
go/src/gui_test/main.go:9:12: undefined: ui.NewEntry
go/src/gui_test/main.go:10:13: undefined: ui.NewButton
go/src/gui_test/main.go:11:15: undefined: ui.NewLabel
go/src/gui_test/main.go:12:10: undefined: ui.NewVerticalBox
go/src/gui_test/main.go:13:14: undefined: ui.NewLabel
go/src/gui_test/main.go:17:13: undefined: ui.NewWindow
go/src/gui_test/main.go:20:26: undefined: ui.Button
go/src/gui_test/main.go:23:26: undefined: ui.Window
go/src/gui_test/main.go:24:4: undefined: ui.Quit
go/src/gui_test/main.go:24:4: too many errors
```