修复编译错误

https://www.bountysource.com/issues/3227190-libxfcegui4-4-10-0-is-broken-when-built-against-libxfce4util-4-11-0-git-with-missing-xfce_setenv
不过……
“libxfcegui4 has been deprecated since 4.8 and was moved to the repository archive ages ago. If you want or need to continue supporting it, you'll have to ship the patch in your distro. We're no longer pushing changes to libxfcegui4, sorry.”