Wepcrackgui should have an option to build ONLY against gtk (gtk-sharp2) or against qt4 (qyoto) toolkit.
For the moment you can't build only against qt4 toolkit because the configure script will search anyway for the package 'gtk-sharp2' :
Looking for required packages
Checking for package 'gtk-sharp-2.0'.. ERROR: Package named 'gtk-sharp-2.0' >= 2.12.10 not found.
Try adjusting your PKG_CONFIG_PATH environment variable.
If this is normal, the file 'Dependencies' on the root directory should be modified to include gtk-sharp-2.0 as a global dependency