std.system reports win32 when running OS X

[Dave Chapman via Digitalmars-d-learn]

I am running an iMac with OS X 10.11.5 (El Capitan) and dmd 
version 2.072.2
The following program prints out OS = win32.

Is this the intended behavior?
#!/usr/local/bin/rdmd

import std.stdio;
import std.system;

void main (string[] args) {
  immutable OS os;
  writefln("OS = %s",os);
}