Original patch from: http://www.cc.rim.or.jp/~yaz/patch.html#audacious
Direct link: http://www.cc.rim.or.jp/~yaz/audacious-1.0.0_yaz.diff.gz

You need to apply this patch _before_ running autogen.sh.

UPDATE: xmms-crossfade-0.3.11 has native Audacious (1.1) support.
        http://www.eisenlohr.org/xmms-crossfade/index.html