vcs.rb: old version cannot refine modules

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62060 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/vcs.rb

@@ -86,18 +86,21 @@ else
         super
       end
     end
-    refine Kernel do
-      def system(*args, exception: true, **opts)
-        STDERR.puts [*args, **opts].inspect if $DEBUG
-        ret = super(*args, **opts, exception: exception)
-        raise "Command failed with status (#$?): #{args[0]}" if exception and !ret
-        ret
-      end
-    end
   ensure
     $VERBOSE = verbose unless verbose.nil?
   end
   using DebugPOpen
+  module DebugSystem
+    def system(*args, exception: true, **opts)
+      STDERR.puts [*args, **opts].inspect if $DEBUG
+      ret = super(*args, **opts, exception: exception)
+      raise "Command failed with status (#$?): #{args[0]}" if exception and !ret
+      ret
+    end
+  end
+  module Kernel
+    prepend(DebugSystem)
+  end
 end
 
 class VCS