COMP: Fix unnecessary wrapping hierarchy file regeneration

https://discourse.vtk.org/t/python-wrapping-is-slow-on-windows/5862/11

Fixes #22

Author: lassoan

CMake/vtkWrapHierarchy.cmake

@@ -146,12 +146,17 @@ $<$<BOOL:$<TARGET_PROPERTY:${module_name},INCLUDE_DIRECTORIES>>:
     set(hierarchy_depends ${OTHER_HIERARCHY_TARGETS})
   endif ()
 
+  # The target depends on ${module_name}Hierarchy.stamp.txt (instead of directly on
+  # ${module_name}Hierarchy.txt) because this ensures that after any of the dependencies
+  # (such as vtkWrapHierarchy.exe) changes, the hierarchy file is regenerated once and exactly once.
   add_custom_command(
-    OUTPUT  "${OUTPUT_DIR}/${module_name}Hierarchy.txt"
+    OUTPUT  ${CMAKE_CURRENT_BINARY_DIR}/${module_name}Hierarchy.stamp.txt
+            "${OUTPUT_DIR}/${module_name}Hierarchy.txt"
     COMMAND ${VTK_WRAP_HIERARCHY_EXE}
             @${_args_file} -o ${OUTPUT_DIR}/${module_name}Hierarchy.txt
             ${module_name}Hierarchy.data
             @${_other_hierarchy_args_file}
+    COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/${module_name}Hierarchy.stamp.txt
     COMMENT "For ${module_name} - updating ${module_name}Hierarchy.txt"
     DEPENDS ${VTK_WRAP_HIERARCHY_EXE}
             ${CMAKE_CURRENT_BINARY_DIR}/${_args_file}
@@ -162,6 +167,6 @@ $<$<BOOL:$<TARGET_PROPERTY:${module_name},INCLUDE_DIRECTORIES>>:
     )
   add_custom_target(${module_name}Hierarchy
     DEPENDS
-      ${OUTPUT_DIR}/${module_name}Hierarchy.txt)
+      ${CMAKE_CURRENT_BINARY_DIR}/${module_name}Hierarchy.stamp.txt)
 
 endmacro()