FindRuby: Use `MSVC_VERSION` instead of `MSVC##`

Modules/FindRuby.cmake

@@ -207,19 +207,19 @@ set(_RUBY_POSSIBLE_LIB_NAMES ruby ruby-static ruby${_RUBY_VERSION_SHORT} ruby${_
 
 if(WIN32)
    set( _RUBY_MSVC_RUNTIME "" )
-   if( MSVC60 )
+   if( MSVC_VERSION EQUAL 1200 )
      set( _RUBY_MSVC_RUNTIME "60" )
    endif()
-   if( MSVC70 )
+   if( MSVC_VERSION EQUAL 1300 )
      set( _RUBY_MSVC_RUNTIME "70" )
    endif()
-   if( MSVC71 )
+   if( MSVC_VERSION EQUAL 1310 )
      set( _RUBY_MSVC_RUNTIME "71" )
    endif()
-   if( MSVC80 )
+   if( MSVC_VERSION EQUAL 1400 )
      set( _RUBY_MSVC_RUNTIME "80" )
    endif()
-   if( MSVC90 )
+   if( MSVC_VERSION EQUAL 1500 )
      set( _RUBY_MSVC_RUNTIME "90" )
    endif()