Revert "third_party/protobuf: Update to HEAD (f52e188fe4)"

third_party/protobuf/src/google/protobuf/stubs/mathutil.h

Index: third_party/protobuf/src/google/protobuf/stubs/mathutil.h
diff --git a/third_party/protobuf/src/google/protobuf/stubs/mathutil.h b/third_party/protobuf/src/google/protobuf/stubs/mathutil.h
index 8a9f69a0b225164b9749d4add91565428ddcd5fd..27956a8ea02f77b98c6c1bfbe98006fb5a7358e9 100644
--- a/third_party/protobuf/src/google/protobuf/stubs/mathutil.h
+++ b/third_party/protobuf/src/google/protobuf/stubs/mathutil.h
@@ -41,6 +41,27 @@ namespace google {
 namespace protobuf {
 namespace internal {
 template<typename T>
+bool IsNan(T value) {
+  return false;
+}
+template<>
+inline bool IsNan(float value) {
+#ifdef _MSC_VER
+  return _isnan(value);
+#else
+  return isnan(value);
+#endif
+}
+template<>
+inline bool IsNan(double value) {
+#ifdef _MSC_VER
+  return _isnan(value);
+#else
+  return isnan(value);
+#endif
+}
+
+template<typename T>
 bool AlmostEquals(T a, T b) {
   return a == b;
 }
@@ -59,7 +80,7 @@ class MathUtil {
  public:
   template<typename T>
   static T Sign(T value) {
-    if (value == T(0) || MathLimits<T>::IsNaN(value)) {
+    if (value == T(0) || ::google::protobuf::internal::IsNan<T>(value)) {
       return value;
     }
     return value > T(0) ? 1 : -1;