onlineupdate: work around GCC7 -Werror=implicit-fallthrough

This is pretty stupid, but oh well...

Change-Id: I1e605b2858a917f61922df757809a2aceb14a914

onlineupdate/source/libmar/tool/mar.c

@@ -327,6 +327,7 @@ int main(int argc, char **argv) {
     printf("\n");
     /* The fall through from 'T' to 't' is intentional */
   }
+  /* Fall through */
   case 't':
     return mar_test(argv[2]);
 

onlineupdate/source/update/updater/updater.cxx

@@ -4234,7 +4234,7 @@ int add_dir_entries(const NS_tchar *dirpath, ActionList *list)
             case FTS_DEFAULT:
                 LOG(("add_dir_entries: found a non-standard file: " LOG_S,
                      ftsdirEntry->fts_path));
-            // Fall through and try to remove as a file
+            /* Fall through */ // and try to remove as a file
 
             // Files
             case FTS_F: