Hmm, I think you are doing it around the wrong way.
No doubt I'm doing stuff wrong, because I'm on very thin ice when trying these things. Will make new attempts to get the trunk running. VMs are very helpful here. Always good to be able to fallback to the safe 4.6 VM when I mess things up.
As for the 4.6 GTK3(alpha) most of my existing code base didn't fare well there. Complied but looked horrible and was mostly useless.
When making new mini programs on alpha there are some color challenges and the Hi-DPI cases don't do well.
If / when I get the trunk to run with GTK3 I'll let you know the results.