mini-os: sort objects in binary archives

mini-os: sort objects in binary archives

When building stubdom the mini-os objects are also linked into the
binary. Unfortunately the linker will place them in the order found in
the archive. Since this order is random the resulting stubdom binary
differs when it was built from identical sources but on different
build hosts. To help with creating a reproducible binary the elements
in an archive must simply be sorted before passing them to $(AR).

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
[ ijc -- massaged paths to apply to external mini-os tree ]