if prototype is declared static make function static to match

Today, a compiler was encountered that considered it an error
to have the prototype declared static and the function body
not

src/allmain.c

@@ -876,7 +876,7 @@ enum earlyarg e_arg;
  *                    optimization so that display output
  *                    can be debugged without buffering.
  */
-void
+STATIC_OVL void
 debug_fields(opts)
 const char *opts;
 {