wmaker: Cleaned dangerous function prototype usage

- remove extern declaration in source file, use header instead

- add inclusion of header defining the functions of the file to
get the compiler to cross-check them

- marked static the functions that should not be visible ouside
their file

src/osdep_darwin.c

@@ -9,6 +9,7 @@
 #include <WINGs/WUtil.h>
 
 #include "wconfig.h"
+#include "funcs.h"
 
 /*
  * copy argc and argv for an existing process identified by `pid'