cmake: Fix compilation for MSVC 2015

snprintf is now available in MSVC 2015!

src/doomtype.h

@@ -100,9 +100,9 @@ typedef long ssize_t;
 
 #if defined (_MSC_VER) || defined (__OS2__)
 	// Microsoft VisualC++
-#ifdef _MSC_VER
+#if (_MSC_VER <= 1800) // MSVC 2013 and back
 	#define snprintf                _snprintf
-#if (_MSC_VER <= 1200)
+#if (_MSC_VER <= 1200) // MSVC 2012 and back
 	#define vsnprintf               _vsnprintf
 #endif
 #endif