patch 8.0.0280: problem setting multi-byte environment var on MS-Windows

Problem:    On MS-Windows setting an environment variable with multi-byte
            strings does not work well.
Solution:   Use wputenv when possible. (Taro Muraoka, Ken Takata)

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    280,
 /**/
     279,
 /**/