A patch preventing gcc3 compilation issues with enabled optimizations was recently commited to libvorbis's cvs tree. See http://bugs.xiph.org/show_bug.cgi?id=271 for more informations about the bug. The patch is at the submitted URL.
I cannot download the patch. Closing as WONTFIX. p.s. Is this still an issue in the latest libvorbis ebuld?
*** Bug 11012 has been marked as a duplicate of this bug. ***