title: meson `get_option()` to find `/etc/dbus-1/system.d/` directory
body: <p>Meson uses <code>get_option('bindir')</code> to find the binary directory, which should be <code>/usr/bin</code> in most cases.</p>
  <p>I have configuration file for d-bus, the file should be like <code>/etc/dbus-1/system.d/&lt;file&gt;.conf</code>, how can I use the similar method to find the path of <code>etc/dbus-1/system.d/</code> in <code>meson.build</code> file?</p>