ext_conf_builder.rb: fix tempfile leak

* lib/rubygems/ext/ext_conf_builder.rb (build): ensure to remove
  temporary siteconf script.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46146 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/ext/ext_conf_builder.rb

@@ -38,11 +38,11 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
           run cmd, results
         ensure
           FileUtils.mv 'mkmf.log', dest_path if File.exist? 'mkmf.log'
+          siteconf.unlink
         end
 
         ENV["DESTDIR"] = nil
         ENV["RUBYOPT"] = rubyopt
-        siteconf.unlink
 
         make dest_path, results