Fixed VS compilation.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@8352 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/irr_driver.cpp

@@ -44,6 +44,11 @@ using namespace irr::core;
 using namespace irr::scene;
 using namespace irr::video;
 
+#ifndef round
+#  define round(x)  (floor(x+0.5f))
+#endif
+
+
 /** singleton */
 IrrDriver *irr_driver = NULL;