VTK_USE_COCOA not set

[samuelgerber]

When building on macOSX the linking step fails with:

[ 21%] Linking CXX shared library /Users/sam/Software/SlicerLookingGlass-build/lib/Slicer-4.13/libvtkRenderingLookingGlass.dylib
Undefined symbols for architecture x86_64:
  "vtkCocoaLookingGlassRenderWindow::SetLGDeviceIndex(int)", referenced from:
      vtkLookingGlassInterface::CreateLookingGlassRenderWindow(int) in vtkLookingGlassInterface.cxx.o
  "vtkCocoaLookingGlassRenderWindow::New()", referenced from:
      vtkLookingGlassInterface::CreateLookingGlassRenderWindow(int) in vtkLookingGlassInterface.cxx.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

The issue appears to be that VTK_USE_COCOA is not set and the files are not included in CMakeLists.txt in the LookingGlassVTKModule here:
https://github.com/Kitware/LookingGlassVTKModule/blob/f3b4c8928c002533337479733af4ec10282c7aa9/CMakeLists.txt#L13

By including the mac specific source files the build works.

This might be related to a warning during the CMake configuration step:

CMake Deprecation Warning at /Users/sam/Software/Slicer-build/VTK-build/lib/cmake/vtk-9.0/vtk-use-file-deprecated.cmake:1 (message):
  The `VTK_USE_FILE` is no longer used starting with 8.90.
Call Stack (most recent call first):
  /Users/sam/Software/Slicer-build/Slicer-build/UseSlicer.cmake:134 (include)
  CMakeLists.txt:23 (include)

[jcfr]

Thanks for the detailed report, root cause has been identified and reported in https://gitlab.kitware.com/vtk/vtk/-/issues/18032

Waiting this is addressed a workaround will be added to the SlicerLookingGlass extension