message: COMP: fix CMake CMP0106 witk RTK_BUILD_DOXYGEN
  Patch based on InsightSoftwareConsortium/ITK@f071cff
diff: -#
  -# Build the documentation
  -#
  -include (${CMAKE_ROOT}/Modules/Documentation.cmake)
  -
  -find_package(Doxygen)
  if(RTK_BUILD_DOXYGEN)
  + find_package(UnixCommands)
  + find_package(Doxygen)
  + find_package(Gnuplot)
  + find_package(HTMLHelp)
  + find_package(Perl)
  + find_package(Wget)
  #
  # Configure the script and the doxyfile, then add target
  