Hi!
Please apply the attached git patch (via git am). It adds support for the
x32 architecture, by linking recipes-x32-efi to recipes-amd64-efi. The
patch can be applied directly to the d-i/partman-auto git repository.
If you want to test, as the patch-set for x32 in d-i involves around twenty
packages, you'll want ready packages from the repository at debian-x32.org.
Complete d-i isos are available at http://debian-x32.org/#debian-installer
while debs/udebs/modified sources at http://ftp.debian-x32.org/debian/