erasure-code: disable SSE extensions

Until jerasure-2 / gf-complete is able to detect them at runtime.

http://tracker.ceph.com/issues/7757 refs #7757

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1489 from dachary/wip-7757

erasure-code: disable SSE extensions

Reviewed-by: Christophe Courtaut <christophe.courtaut@gmail.com>