Hard-code the _WIN32_WINNT_VISTA value.

Maybe Borland is also using pre-vista headers?

src/xpdev/genwrap.c

@@ -1155,7 +1155,7 @@ int64_t xp_fast_timer64(void)
 	else
 		ret = -1;
 #elif defined(_WIN32)
-#if _WIN32_WINNT < _WIN32_WINNT_VISTA
+#if WINVER < 0x0600
 	ret=GetTickCount() / 1000;
 #else
 	ret=GetTickCount64() / 1000;