Add support for CMAKE_CROSSCOMPILING_EMULATOR
Same principle as vtk/vtk@d767f09b but for Paraview:
This commit updates the build systems to allow cross-compiling VTK using toolchain defining CMAKE_CROSSCOMPILING_EMULATOR.
It simplifies the cross-compilation removing the need to independently compile the "VTKCompileTools".
see also vtk/vtk@d0f83dfe
Edited by Mathieu Westphal (Kitware)