Detect and check for CMOV.

Some MMX-only CPUs do not have support for CMOV.
All SSE/MMX2 CPUs should be fine, thus no check was
added to those functions.
See also https://sourceforge.net/tracker/?func=detail&aid=3358347&group_id=205275&atid=992986

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
