build: move --with-intl to intl optgroup

PR-URL: https://github.com/iojs/io.js/pull/1680
Reviewed-By: Rod Vagg <rod@vagg.org>

configure

@@ -237,7 +237,7 @@ parser.add_option('--with-etw',
     dest='with_etw',
     help='build with ETW (default is true on Windows)')
 
-parser.add_option('--with-intl',
+intl_optgroup.add_option('--with-intl',
     action='store',
     dest='with_intl',
     default='none',