Make v8 compile on VS2013.

src/win32-math.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 19 matching lines @@
 // semantics for these functions.
 // (http://www.opengroup.org/onlinepubs/000095399/)
 
 #ifndef V8_WIN32_MATH_H_
 #define V8_WIN32_MATH_H_
 
 #ifndef _MSC_VER
 #error Wrong environment, expected MSVC.
 #endif  // _MSC_VER
 
+// MSVC 2013+ provides implementations of all standard math functions.
+#if (_MSC_VER < 1800)
 enum {
   FP_NAN,
   FP_INFINITE,
   FP_ZERO,
   FP_SUBNORMAL,
   FP_NORMAL
 };
 
 
 namespace std {
 
 int isfinite(double x);
 int isinf(double x);
 int isnan(double x);
 int isless(double x, double y);
 int isgreater(double x, double y);
 int fpclassify(double x);
 int signbit(double x);
 
 }  // namespace std
 
+#endif  // _MSC_VER < 1800
+
 #endif  // V8_WIN32_MATH_H_