IO factories in external module fails at configuration

[SimonRit]

Description

Trying to compile RTK externally after compiling the latest ITK main. I get the following error at configuration

CMake Error at /home/srit/src/itk/itk/CMake/ITKModuleMacros.cmake:429 (target_link_libraries):
  Cannot specify link libraries for target "ITKImageIO" which is not built by
  this project.
Call Stack (most recent call first):
  /home/srit/src/itk/itk/CMake/ITKModuleExternal.cmake:202 (itk_module_impl)
  CMakeLists.txt:258 (include)

This is likely caused by #5721.

Steps to Reproduce

Compile ITK.
Then download RTK and configure RTK separately.

Expected behavior

Configuration of the project.

Actual behavior

Fails with the above error

Reproducibility

100%

Versions

Latest ITK in the main branch, Ubuntu.

[SimonRit]

Sorry @blowekamp, I don't know how to solve this...

[blowekamp]

I only tested RTK when is was enabled as part of the ITK build. This is RTK built against a build directory of ITK?

[SimonRit]

Yes exactly. And the problem disappears if I comment out the following lines
https://github.com/RTKConsortium/RTK/blob/main/itk-module.cmake#L53-L61
I just tested ITKIOScanco and there is the same problem so it's probably preferable to use this as a smaller test.

[SimonRit]

Fixed by #5763.