Fix some error when merging with grub2-cur 修复一些合并 grub2-cur 时的错误
1. Add back the grub_target_to_host* and grub_host_to_target* defines
   重新加回 grub_target_to_host* 和 grub_host_to_target* 等的 define
2. Add back the function grub_strcmp
   重新加回函数 grub_strcmp