overdue refactor: compile all watch modules separately

watch-library/watch/watch_slcd.h

@@ -21,8 +21,12 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
+#ifndef _WATCH_SLCD_H_INCLUDED
+#define _WATCH_SLCD_H_INCLUDED
 ////< @file watch_slcd.h
 
+#include "watch.h"
+
 /** @addtogroup slcd Segment LCD Display
   * @brief This section covers functions related to the Segment LCD display driver, which is responsible
   *        for displaying strings of characters and indicators on the main watch display.
@@ -100,3 +104,4 @@ void watch_clear_indicator(WatchIndicatorSegment indicator);
 void watch_clear_all_indicators();
 
 /// @}
+#endif