wxWidgets 2.8.x under windows does not support 64 bit.
wxWidgets 2.9.x under windows does support 64 bit; but, Code::Blocks still has 64 bit compile issues and crashes on shutdown with wxWidgets 2.9.x when 32 bit build is used.
Edit: When wxWidgets 3.0 is released is likely when Code::Blocks will start to switch over to wxWidgets higher than 2.8.
Note: wxWidgets 2.9.x is an development build not recommend for production use.
Edit: Another stopper is MinGW GCC does not officially support 64 bit builds. This is only a minor stopper since TDM MinGW-like GCC does support 64 bit builds under windows.