Set softtabstop to -1 to allow easy sw configuraton

ftdetect/polyglot.vim

@@ -2770,6 +2770,13 @@ if !has_key(s:disabled_packages, 'autoindent')
     if shiftwidth > 0
       setlocal expandtab
       let &l:shiftwidth=shiftwidth
+      try
+        " Sunchronize tabstop with shiftwidth
+        let &l:softtabstop = -1
+      catch /^Vim\%((\a\+)\)\=:E487/ 
+        " -1 was not supported before Vim 7.4
+        let &l:softtabstop = a:num_spaces
+      endtry
       let &l:softtabstop=shiftwidth
       return 1
     endif