* Added new macros to vtkModuleMacros.cmake to add targets for build-tools. Now
  any component/module creating a tool that's used at compile time should use
  the vtk_compile_tools_target() macro.
* vtk_compile_tools_target(), besides ensuring that the target properties are
  setup properly, adds the target to the VTK_COMPILETOOLS_TARGETS list.
* As a last step, VTK_COMPILETOOLS_TARGETS are exported to both VTKTargets.cmake
  and VTKCompileToolsConfig.cmake.
* When cross compiling VTKCompileToolsConfig.cmake is imported to load
  information about all the build tools.
* vtkCompileTools is a new virtual target that can be used to build host-tools.
  It includes all the targets exported using vtk_compile_tools_target() or
  vtk_compile_tools_target_export() macros.
* For projects, like ParaView, that contain VTK, added a mechanism for the
  parent project to manage importing of the compile tools when cross compiling.

Change-Id: Ibf38868d8ea5f562c7c2682936c72bc11208c5c9