message: Fix build without CAF::io target
diff: add_custom_target(all_tools)
  -include_directories(${LIBCAF_INCLUDE_DIRS})
  -
  macro(add name)
  add_executable(${name} ${name}.cpp ${ARGN})
  - target_link_libraries(${name} CAF::core CAF::io)
  - install(FILES ${name}.cpp DESTINATION ${CMAKE_INSTALL_DATADIR}/caf/tools/${folder})
  + install(FILES ${name}.cpp DESTINATION ${CMAKE_INSTALL_DATADIR}/caf/tools)
  add_dependencies(${name} all_tools)
  endmacro()
  +add(caf-vec)
  +target_link_libraries(caf-vec PRIVATE CAF::core)
  +
  +if(TARGET CAF::io)
  if(WIN32)
  message(STATUS "skip caf-run (not supported on Windows)")
  else()
  add(caf-run)
  + target_link_libraries(caf-run PRIVATE CAF::io CAF::core)
  + endif()
  endif()
  -
  -add(caf-vec)
  