patch 8.0.1688: some macros are used without a semicolon

Problem:    Some macros are used without a semicolon, causing auto-indent to be
            wrong.
Solution:   Use the do-while(0) trick. (Ozaki Kiichi, closes #2729)

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1688,
 /**/
     1687,
 /**/