undo removal of alloca in builtinimport.c

Author: dhalbert

py/builtinimport.c

@@ -330,7 +330,7 @@ mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
         }
 
         uint new_mod_l = (mod_len == 0 ? (size_t)(p - this_name) : (size_t)(p - this_name) + 1 + mod_len);
-        char new_mod[new_mod_l];
+        char *new_mod = alloca(new_mod_l);
         memcpy(new_mod, this_name, p - this_name);
         if (mod_len != 0) {
             new_mod[p - this_name] = '.';