Added INT16_MIN and INT16_MAX for MSVC builds

These macros were not defined in earlier version of MSVC

Change-Id: I8270a3abb7c6e9ead1931a653d7e41f877a1017b

vpx/vpx_integer.h

@@ -28,6 +28,8 @@ typedef unsigned int   uint32_t;
 typedef signed __int64   int64_t;
 typedef unsigned __int64 uint64_t;
 #define INT64_MAX _I64_MAX
+#define INT16_MAX _I16_MAX
+#define INT16_MIN _I16_MIN
 #endif
 
 #ifndef _UINTPTR_T_DEFINED