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

See issue #699.

py/objboundmeth.c

@@ -37,6 +37,7 @@ typedef struct _mp_obj_bound_meth_t {
 
 #if MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_DETAILED
 STATIC void bound_meth_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
+    (void)kind;
     mp_obj_bound_meth_t *o = o_in;
     print(env, "<bound_method %p ", o);
     mp_obj_print_helper(print, env, o->self, PRINT_REPR);