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

See issue #699.
diff --git a/py/objstr.c b/py/objstr.c
index 55d4cbf..2aea44b 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -132,6 +132,8 @@
 
 #if !MICROPY_PY_BUILTINS_STR_UNICODE || MICROPY_CPYTHON_COMPAT
 STATIC mp_obj_t str_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;
+
 #if MICROPY_CPYTHON_COMPAT
     if (n_kw != 0) {
         mp_arg_error_unimpl_kw();
@@ -171,6 +173,8 @@
 #endif
 
 STATIC mp_obj_t bytes_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;
+
     if (n_args == 0) {
         return mp_const_empty_bytes;
     }