Replace #pragma once with #ifndef #define #endif logic because #pragma once does not work cleanly on OSX

include/usage.h

@@ -3,7 +3,10 @@
  * License.....: MIT
  */
 
-#pragma once
+#ifndef _USAGE_H
+#define _USAGE_H
 
 void usage_mini_print (const char *progname);
 void usage_big_print  (const char *progname);
+
+#endif // _USAGE_H