Visual Studio provides stdint.h these days.

include/v8stdint.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Load definitions of standard types.
 
 #ifndef V8STDINT_H_
 #define V8STDINT_H_
 
 #include <stddef.h>
+#include <stdint.h>
 #include <stdio.h>
 
 #include "v8config.h"
 
-#if V8_OS_WIN && !V8_CC_MINGW
-
-typedef signed char int8_t;
-typedef unsigned char uint8_t;
-typedef short int16_t;  // NOLINT
-typedef unsigned short uint16_t;  // NOLINT
-typedef int int32_t;
-typedef unsigned int uint32_t;
-typedef __int64 int64_t;
-typedef unsigned __int64 uint64_t;
-// intptr_t and friends are defined in crtdefs.h through stdio.h.
-
-#else
-
-#include <stdint.h>  // NOLINT
-
-#endif
-
 #endif  // V8STDINT_H_