vtkm: skip installing headers if VTK is configured to do so

ThirdParty/vtkm/vtkvtkm/CMakeLists.txt

@@ -27,6 +27,12 @@ set(VTKm_BUILD_CMAKE_BASE_DIR "${CMAKE_BINARY_DIR}")
 set(VTKm_INSTALL_CONFIG_DIR "${_vtk_build_CMAKE_DESTINATION}/vtkm")
 set(VTKm_INSTALL_CMAKE_MODULE_DIR "${VTKm_INSTALL_CONFIG_DIR}/cmake")
 
+if (_vtk_build_INSTALL_HEADERS)
+  set(VTKm_INSTALL_ONLY_LIBRARIES OFF)
+else ()
+  set(VTKm_INSTALL_ONLY_LIBRARIES ON)
+endif ()
+
 set(VTKm_USE_DEFAULT_SYMBOL_VISIBILITY OFF)
 set(VTKm_ENABLE_RENDERING OFF)
 set(VTKm_ENABLE_TESTING OFF)