protobuf build documenting: move the WITH_PROTOBUF option to the top level

CMakeLists.txt

@@ -279,6 +279,7 @@ OCV_OPTION(WITH_GDAL           "Include GDAL Support"                        OFF
 OCV_OPTION(WITH_GPHOTO2        "Include gPhoto2 library support"             ON   IF (UNIX AND NOT ANDROID AND NOT IOS) )
 OCV_OPTION(WITH_LAPACK         "Include Lapack library support"              (NOT CV_DISABLE_OPTIMIZATION)  IF (NOT ANDROID AND NOT IOS) )
 OCV_OPTION(WITH_ITT            "Include Intel ITT support"                   ON   IF (NOT APPLE_FRAMEWORK) )
+OCV_OPTION(WITH_PROTOBUF       "Enable libprotobuf"                          ON )
 
 # OpenCV build components
 # ===================================================

cmake/OpenCVFindProtobuf.cmake

 # If protobuf is found - libprotobuf target is available
 
-ocv_option(WITH_PROTOBUF "Enable libprotobuf" ON)
-ocv_option(BUILD_PROTOBUF "Force to build libprotobuf from sources" ON)
-ocv_option(PROTOBUF_UPDATE_FILES "Force rebuilding .proto files (protoc should be available)" OFF)
-
 set(HAVE_PROTOBUF FALSE)
 
 if(NOT WITH_PROTOBUF)
   return()
 endif()
 
+ocv_option(BUILD_PROTOBUF "Force to build libprotobuf from sources" ON)
+ocv_option(PROTOBUF_UPDATE_FILES "Force rebuilding .proto files (protoc should be available)" OFF)
+
 function(get_protobuf_version version include)
   file(STRINGS "${include}/google/protobuf/stubs/common.h" ver REGEX "#define GOOGLE_PROTOBUF_VERSION [0-9]+")
   string(REGEX MATCHALL "[0-9]+" ver ${ver})