overdue refactor: compile all watch modules separately

watch-library/watch/watch_private.h

@@ -21,10 +21,17 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
+#ifndef _WATCH_PRIVATE_H_INCLUDED
+#define _WATCH_PRIVATE_H_INCLUDED
+
+#include "watch.h"
 
 /// Called by main.c while setting up the app. You should not call this from your app.
 void _watch_init();
 
+/// Initializes the real-time clock peripheral.
+void _watch_rtc_init();
+
 /// Called by buzzer and LED setup functions. You should not call this from your app.
 void _watch_enable_tcc();
 
@@ -33,3 +40,4 @@ void _watch_disable_tcc();
 
 /// Called by main.c if plugged in to USB. You should not call this from your app.
 void _watch_enable_usb();
+#endif