patch 8.0.1351: warning for unused variables building with MinGW

Problem:    Warning for unused variables building with MinGW.
Solution:   Change a few #ifdefs (suggested by John Marriott). Remove
            superfluous checks of FEAT_MBYTE.
diff --git a/src/version.c b/src/version.c
index 066294a..14e5083 100644
--- a/src/version.c
+++ b/src/version.c
@@ -772,6 +772,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1351,
+/**/
     1350,
 /**/
     1349,