I'm currently using a method where I have a "base" file that defines the types, interfaces and a basic API for the package. I then create an _windows.go and _linux.go file and add platform specific types that I can apply the interface to. The setup is basically like this: http://play.golang.org/p/2DJxTuSAIh.
The use of interfaces is an orthogonal concept. Use an interface where an interface makes sense, but it's often simpler just provide an implementation by the same name in the proper GOOS and GOARCH files.
The method of using a common constructor name (from your example) is also used in places in the std lib, as is the method of assigning a global variable name to a function (which is similar in concept to the former method).
Because Go is statically typed, and you can't redeclare global identifiers, the build system will always catch problems; it's just a matter of testing for all applicable systems to ensure that no OS or ARCH has an out of date implementation.