patch 8.0.0840: MS-Windows: fopen() and open() prototypes are wrong

Problem:    MS-Windows: fopen() and open() prototypes do not match the ones in
            the system header file.  Can't build without FEAT_MBYTE.
Solution:   Add "const".  Move macro to after including protoo.h.

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    840,
 /**/
     839,
 /**/