testConsoleBuf: tighten the check for the /utf-8 flag

It appears that Visual Studio 2015 Update 1 lacks this flag. Update 3
includes it; Update2 is unknown.

See cmake/cmake#16623.

CMakeLists.txt

@@ -946,7 +946,7 @@ IF(KWSYS_STANDALONE OR CMake_SOURCE_DIR)
         testConsoleBuf
         )
       IF("x${CMAKE_CXX_COMPILER_ID}" STREQUAL "xMSVC" AND
-         NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS "19.0")
+         CMAKE_CXX_COMPILER_VERSION VERSION_GREATER "19.0.23506")
         set_property(SOURCE testConsoleBuf.cxx testConsoleBufChild.cxx PROPERTY COMPILE_FLAGS /utf-8)
       ENDIF()
       SET_PROPERTY(SOURCE testConsoleBuf.cxx APPEND PROPERTY COMPILE_DEFINITIONS