Found the problem. You will need to replace all instances of TQT_INCLUDE_DIRS with TQT_INCLUDEDIR in all of your CMakeLists.txt files.
After posting my last response I noticed you had typed TQT_INCLUDEDIR and not TQT_INCLUDE_DIR. I did not know whether that was intentional or a typo. Regardless, I modified my patch and built again using TQT_INCLUDEDIR.
The package built. :)
Now, is this a Slackware issue or global?
There are two other patches I need to build kdevelop. I would like to know if this specific fix is global before I submit a bug report.
Darrell