The defintion of ITK_EXPORT was empty in all cases
This has been identified since 2003 as not being necessary for builds. see https://issues.itk.org/jira/browse/ITK-3110
On Windows builds that need exports, they must be unique per library, and that is not controlled by CMake now.
The PrintSelfCheck.tcl was the only remenant need for This patch, and that is no longer being used, so that file as been removed.
The ITK_EXPORT define was set to nothing and had no known remaining purpose. It was removed to make the over all code easier to understand. There was, understandably, a bit of confusion about the need for this being pervasive in the code.
It is currently backwards compatible to have this in code, but at some future point it will be removed.