Beware if using GLib < 2.55.1

[Aleksander Morgado]

Hey!

If you are using a GLib version < 2.55.1, please make sure you have
backported the following patch in your system:
https://gitlab.gnome.org/GNOME/glib/commit/37d9b0c6995f97ea0f744650aaf5179081f878ba

Without that patch, there are certain conditions that may trigger a
very bad memory leak in the MM daemon. E.g. if you enable GPS raw/nmea
sources and then you poll querying with mmcli --location-get, the leak
would be triggered and MM may end up consuming a lot of memory pretty
quickly.

I've also added a note in MM's configure.ac warning about this.

-- 
Aleksander
https://aleksander.es