darwin_specific.c: unused warning fix.

src/misc/darwin_specific.c

@@ -76,6 +76,7 @@ static CFArrayRef copy_all_locale_indentifiers(void)
  *****************************************************************************/
 void system_Init( libvlc_int_t *p_this, int *pi_argc, const char *ppsz_argv[] )
 {
+    VLC_UNUSED(p_this);
     char i_dummy;
     char *p_char = NULL;
     char *p_oldchar = &i_dummy;