I don't know if CodeBlocks can use the monolithic library out-of-the-box or how to make it use it, so far i was always using the individual libraries because that is how the systems i used provided wxWidgets, but basically you have to supply the path of the wx-config script to the configure script of CodeBlocks. With your setup this would be something like this:
./configure --with-wx-config=/opt/wx/3.1.3/bin/wx-config