After a few time, I found some time to come back on libc6-xen.
It looks like a bit complicated to extract all the patches from the
fedora glibc, but it looks like those patches are included in glibc 2.4.
That's why I propose to have a libc6-xen with the same path as
libc6-i686, and which conflicts with it. When installed it will be
activated on i686 class processors, which, if I am right, are the
minimum processors supported by Xen.
Does it looks ok to you?
I have made some test packages, available on:
http://people.debian.org/~aurel32/xen