Move the msvc round() replacement to msvc.h

Change-Id: If470411c3c62a27f52261f4ece2c5054b71789c7
diff --git a/vpx_ports/msvc.h b/vpx_ports/msvc.h
index 43a36e7..b08d216 100644
--- a/vpx_ports/msvc.h
+++ b/vpx_ports/msvc.h
@@ -18,5 +18,14 @@
 #  define snprintf _snprintf
 # endif  // _MSC_VER < 1900
 
+#if _MSC_VER < 1800  // VS2013 provides round
+static INLINE double round(double x) {
+  if (x < 0)
+    return ceil(x - 0.5);
+  else
+    return floor(x + 0.5);
+}
+#endif  // _MSC_VER < 1800
+
 #endif  // _MSC_VER
 #endif  // VPX_PORTS_MSVC_H_