Changes of c0b0562533 to common code broke
wxGTK1 build, as wx/gtk/private/wrapgtk.h is for wxGTK 2+ only.
Fix this by handling wxGTK 1 separately and including gtk/gtk.h directly
for it.
Hopefully this code will be removed, together with the rest of wxGTK1
support, in some not so distant future.
