Fix floating point issues on Windows.

runtime/platform/c99_support_win.h

Index: runtime/platform/c99_support_win.h
diff --git a/runtime/platform/c99_support_win.h b/runtime/platform/c99_support_win.h
index 1d09eff6a7b7843931c4d5b026f24bd918f873d7..10fcf2bec1e9cd16042e2f09a5546b4d85d038fc 100644
--- a/runtime/platform/c99_support_win.h
+++ b/runtime/platform/c99_support_win.h
@@ -48,10 +48,19 @@ static inline double trunc(double x) {
 }
 
 static inline double round(double x) {
-  if (x < 0) {
-    return ceil(x - 0.5);
+  if (!_finite(x)) {
+    return x;
+  }
+
+  double intpart;
+  double fractpart = modf(x, &intpart);
+
+  if (fractpart >= 0.5) {
+    return intpart + 1;
+  } else if (fractpart > -0.5) {
+    return intpart;
   } else {
-    return floor(x + 0.5);
+    return intpart - 1;
   }
 }