Rather than reading the Glade file path from environment variable or command line option, I'd rather use [GResources](https://developer.gnome.org/gio/stable/GResource.html) to compile the GtkBuilder into the main binary. This is how I would've done it originally but it didn't exist yet, and so would have required using non-standard build tools (ex. `exo-csource` or custom script). Now that it exists and Geany is already depending on a new-enough Glib to use GResources, IMO this is the way to go and the recommended approach for GTK+ UI definitions AFAIK.