vpath.rb: no rbconfig.rb

* tool/vpath.rb (VPath#list): no rbconfig.rb, to get rid of cyclic
  dependency.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39134 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/vpath.rb

@@ -66,12 +66,13 @@ class VPath
   end
 
   def list
-    @separator ||= (require 'rbconfig'; RbConfig::CONFIG["PATH_SEPARATOR"])
     @additional.reject! do |dirs|
       case dirs
       when String
         @list << dirs
       when Array
+        raise "--path-separator option is needed for vpath list" unless @separator
+        # @separator ||= (require 'rbconfig'; RbConfig::CONFIG["PATH_SEPARATOR"])
         @list.concat(dirs[0].split(@separator))
       end
       true