Use dedicated CRT function to round the value for MSVS 2015+

round() is available since at least VS 2015. It is not available in
VS 2010. VS 2012 and 13 need to be checked.

include/wx/math.h

@@ -117,7 +117,7 @@
         wxASSERT_MSG(x > (double)INT_MIN - 0.5 && x < (double)INT_MAX + 0.5,
             wxT("argument out of supported range"));
 
-#if defined(HAVE_ROUND) || defined(__VISUALC__)
+#if defined(HAVE_ROUND) || wxCHECK_VISUALC_VERSION(14)
         return int(round(x));
 #else
         return (int)(x < 0 ? x - 0.5 : x + 0.5);