Weird. I don't know why I don't have these problems. The missing gdk-pixbuf includes might be due newer GTK version you used. I build Geany on Windows with GTK 2.16 which was the recommended version since they changed quite some stuff in 2.18. Not sure what's the current status about this.
IIUC GTK for windows remained unrepaired from 2.18 until someone outside the GTK team did a lot of fixes for 2.24.
Cheers Lex