Merge pull request #12901 from alalek:cmake_unsupported_option_warning

cmake/OpenCVUtils.cmake

@@ -605,10 +605,12 @@ macro(OCV_OPTION variable description value)
       option(${variable} "${description}" ${__value})
     endif()
   else()
-    if(DEFINED ${variable})
-      # TODO: message(WARNING "Option will be ignored: ${variable} (=${${variable}})")
+    if(DEFINED ${variable} AND NOT OPENCV_HIDE_WARNING_UNSUPPORTED_OPTION)
+      message(WARNING "Unexpected option: ${variable} (=${${variable}})\nCondition: IF (${__condition})")
+    endif()
+    if(OPENCV_UNSET_UNSUPPORTED_OPTION)
+      unset(${variable} CACHE)
     endif()
-    unset(${variable} CACHE)
   endif()
   unset(__condition)
   unset(__value)