title: golang error: reference to undefined identifier ‘syscall.TUNSETIFF’
body: <p>So, I have been trying to build flannel (<a href="https://github.com/coreos/flannel" rel="nofollow">https://github.com/coreos/flannel</a>) with gccgo. Here is the error I am getting while building:</p>
  
  <pre><code>$ ./build 
  Building flanneld...
  # github.com/coreos/flannel/pkg/ip
  gopath/src/github.com/coreos/flannel/pkg/ip/tun.go:57:37: error: reference to undefined identifier ‘syscall.TUNSETIFF’
    err = ioctl(int(tun.Fd()), syscall.TUNSETIFF, uintptr(unsafe.Pointer(&amp;ifr)))
                                       ^
  </code></pre>
  
  <p>I am using gccgo-5 and gcc-5. Can anyone please help me figure out what exactly is the issue here? TIA</p>