I've now compiled up kernel 2.6.18.8 supplied with the xen source, and it works correctly with hwcap 0 nosegneg, so It does look like an issue with the xen kernel not setting the hwcap correctly, as opposed to an issue with glibc.
I've now compiled up kernel 2.6.18.8 supplied with the xen source, and it works correctly with hwcap 0 nosegneg, so It does look like an issue with the xen kernel not setting the hwcap correctly, as opposed to an issue with glibc.