message: cmake: update timestamp status
  avoid unnecessary rebuilding of OpenCV libraries
  use timestamp of the first launch of CMake
  to return to previous behavior use `-UOPENCV_TIMESTAMP` CMake option
diff: @@ -917,11 +917,15 @@ endif()
  # ========================== build platform ==========================
  status("")
  status(" Platform:")
  -if(NOT CMAKE_VERSION VERSION_LESS 2.8.11 AND NOT BUILD_INFO_SKIP_TIMESTAMP)
  - string(TIMESTAMP TIMESTAMP "" UTC)
  - if(TIMESTAMP)
  - status(" Timestamp:" ${TIMESTAMP})
  +if(NOT DEFINED OPENCV_TIMESTAMP
  + AND NOT CMAKE_VERSION VERSION_LESS 2.8.11
  + AND NOT BUILD_INFO_SKIP_TIMESTAMP
  +)
  + string(TIMESTAMP OPENCV_TIMESTAMP "" UTC)
  + set(OPENCV_TIMESTAMP "${OPENCV_TIMESTAMP}" CACHE STRING "Timestamp of OpenCV build configuration" FORCE)
  endif()
  +if(OPENCV_TIMESTAMP)
  + status(" Timestamp:" ${OPENCV_TIMESTAMP})
  endif()
  status(" Host:" ${CMAKE_HOST_SYSTEM_NAME} ${CMAKE_HOST_SYSTEM_VERSION} ${CMAKE_HOST_SYSTEM_PROCESSOR})
  if(CMAKE_CROSSCOMPILING)
  