rustc: Enable #[cfg(windows)] and #[cfg(unix)]

src/rustc/driver/driver.rs

@@ -49,6 +49,7 @@ fn default_configuration(sess: session, argv0: str, input: input) ->
     };
 
     ret [ // Target bindings.
+         attr::mk_word_item(os::family()),
          mk("target_os", os::sysname()),
          mk("target_family", os::family()),
          mk("target_arch", arch),

src/test/run-pass/cfg-family.rs

@@ -0,0 +1,7 @@
+#[cfg(windows)]
+fn main() {
+}
+
+#[cfg(unix)]
+fn main() {
+}