Corner case existed when building a cross-arch container (i686 on x86_64)
on a cross-distro host (Fedora container on Ubuntu host).  Fixed the
arch "fixup" code to do the right thing when running from the bootstrap.
Signed-off-by: Michael H. Warfield <mhw@WittsEnd.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>