py, unix: Allow to compile with -Wunused-parameter.

See issue #699.
diff --git a/py/objbool.c b/py/objbool.c
index 6dd9e7f..d60dc8c 100644
--- a/py/objbool.c
+++ b/py/objbool.c
@@ -53,6 +53,7 @@
 }
 
 STATIC mp_obj_t bool_make_new(mp_obj_t type_in, mp_uint_t n_args, mp_uint_t n_kw, const mp_obj_t *args) {
+    (void)type_in;
     mp_arg_check_num(n_args, n_kw, 0, 1, false);
 
     switch (n_args) {