There was an issue with the logic for resolving opaque types that misses
some types due to not comparing C types with opaque type name.
This is now fixed and all Gtk3 units now compile without any manual
modification.
Tested with
43cac7495f
using
`./gir2pas/gir2pas -i gir-rs-files/Gtk-3.0.gir -o gtk3-test-enums -e Enum`