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

See issue #699.
diff --git a/py/objfun.c b/py/objfun.c
index 8f83572..28706cc 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -116,6 +116,7 @@
 
 #if MICROPY_CPYTHON_COMPAT
 STATIC void fun_bc_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind) {
+    (void)kind;
     mp_obj_fun_bc_t *o = o_in;
     print(env, "<function %s at 0x%x>", mp_obj_fun_get_name(o), o);
 }