build: Bump GLib dependency to 2.50 and add guards
libfprint already uses G_DEBUG_HERE in a lot of places which requires GLib 2.50. Also add the appropriate defines so that usage of newer API will result in warnings.
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
libfprint already uses G_DEBUG_HERE in a lot of places which requires GLib 2.50. Also add the appropriate defines so that usage of newer API will result in warnings.