get rid of "implicit fallthrough" warnings with gcc 7

Author: John Peacock

CHANGES

@@ -4,6 +4,10 @@ This is not a complete list of changes.  See repository for full details:
 
     https://bitbucket.org/jpeacock/version (primary)
 
+0.9921 - 2018-04-##
+  * Silence overly compulsive GCC 7 warning
+	https://rt.cpan.org/Ticket/Display.html?id=123477
+
 0.9919 - 2018-04-08
 
   * Core improvements to locale handling

vutil/vxs.inc

@@ -219,7 +219,7 @@ VXS(version_new)
         SvGETMAGIC(vs);
         if(SvOK(vs))
             break;
-        /* drop through */
+        /* fall through */
     case 1:
         /* no param or explicit undef */
         /* create empty object */