MacOSX support
In order to support MacOSX with the Superbuild mechanism, a few extra CMake variables will need to be added [1], configured [2], and passed to the inner-build [3]
A few hard-coded library names will need to be updated [4][5]
[1] https://github.com/KitwareMedical/ITKTubeTK/blob/master/CMake/Superbuild/CMakeLists.txt#L61-L68
[2] https://github.com/KitwareMedical/ITKTubeTK/blob/master/CMake/TubeTKBlockSetCMakeOSXVariables.cmake
[3] https://github.com/KitwareMedical/ITKTubeTK/blob/master/CMake/Superbuild/CMakeLists.txt#L173
[4] https://gitlab.kitware.com/biogears/biogears/blob/master/cmake/ExternalDependencies.cmake#L172-190
[5] https://gitlab.kitware.com/biogears/biogears/blob/master/cmake/ExternalDependencies.cmake#L69-92