Vtk: add option to build examples(#42022)

var/spack/repos/builtin/packages/vtk/package.py

@@ -56,6 +56,7 @@ class Vtk(CMakePackage):
     variant("xdmf", default=False, description="Build XDMF file support")
     variant("ffmpeg", default=False, description="Build with FFMPEG support")
     variant("mpi", default=True, description="Enable MPI support")
+    variant("examples", default=False, description="Enable building & installing the VTK examples")
 
     patch("gcc.patch", when="@6.1.0")
     # patch to fix some missing stl includes
@@ -474,4 +475,6 @@ def cmake_args(self):
                 ]
             )
 
+        cmake_args.append(self.define_from_variant("VTK_BUILD_EXAMPLES", "examples"))
+
         return cmake_args