Fixed VS compilation.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/branches/uni@13564 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/guiengine/widgets/rating_bar_widget.cpp

@@ -25,6 +25,9 @@
 #include <IGUIElement.h>
 #include <IGUIButton.h>
 #include <cmath>
+#ifndef round
+#  define round(x)  (floor(x+0.5f))
+#endif
 
 using namespace GUIEngine;
 using namespace irr::core;