CMake fails with "No file named External_ITK.cmake"

[Xingorno]

When trying to build this extension with Slicer f9bd656dc616e85d8997aec66b338aa990890c59 superbuild configuring fails with a missing External_ITK.cmake

If I remove ITK (and VTK) from the various External_XYZ.cmake in the superbuild folder, I am able to progress.

By default, Slicer's ITK does not build the Ultrasound module, this had to be enabled and built manually. Once everything built, it loaded successfully.

No follow up required.