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.
diff --git a/src/version.c b/src/version.c
index 1922837..d4a334d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    840,
+/**/
     839,
 /**/
     838,