io/console: set HAVE_RB_SCAN_ARGS_OPTIONAL_HASH

* ext/io/console/extconf.rb: obtain optional hash by rb_scan_args() by
  default right now.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39271 b2dd03c8-39d4-4d8f-98ff-823fe69b080e