clang: Don't use mmx nor sse

clang: Don't use mmx nor sse

clang is much more trigger happy than gcc on those.

Change-Id: Ie7c219de3cc26675692eab7361a4ad551f1c65a7
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/786
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>