package ui should not allow building with ancient Go versions that would error out anyway (assuming cgo will let us do that in the first place)

Hi,

I'm not sure where to start with this,

```
$ go get github.com/andlabs/ui
package github.com/andlabs/ui
imports github.com/andlabs/ui
imports github.com/andlabs/ui: /home/jdb/workspaces/go/src/github.com/andlabs/ui/link_linux_amd64.go: malformed #cgo argument: ${SRCDIR}/libui_linux_amd64.a
```

```
$ go version
go version go1.2.1 linux/amd64
```

Could someone please advise on a next step?