How to build on Windows; how to get contents of a file from <input type="file"> as a []byte?

```
src/syscall/syscall_nonlinux.go:5:18: undeclared name: SYS_EXIT
/src/syscall/syscall.go:53:39: too few arguments in call to Syscall
```
I'm using Windows and go1.10. I'm trying to build (`gopherjs build`) this code:

```
package main
//go:generate gopherjs build main.go -o js/app.js -m
// +build ignore

import (
  "log"
)

func main() {
    log.Println("Hello World")
}
```