wscript: Make ADDON_DIR also a conf env variable

In new waf, defines are no longer added to the conf environment, they
only end up in config.h. Consequently, they can't be referenced later
from the wscript.

So explicitly put ADDON_DIR to conf.env.

wscript

@@ -203,7 +203,8 @@ def configure(conf):
     conf.define('CLIENT_NUM', Options.options.clients)
     conf.define('PORT_NUM_FOR_CLIENT', Options.options.application_ports)
 
-    conf.define('ADDON_DIR', os.path.normpath(os.path.join(conf.env['LIBDIR'], 'jack')))
+    conf.env['ADDON_DIR'] = os.path.normpath(os.path.join(conf.env['LIBDIR'], 'jack'))
+    conf.define('ADDON_DIR', conf.env['ADDON_DIR'])
     conf.define('JACK_LOCATION', os.path.normpath(os.path.join(conf.env['PREFIX'], 'bin')))
     conf.define('USE_POSIX_SHM', 1)
     conf.define('JACKMP', 1)