libevas: disable sse3 optimizations for host builds

There's not really any advantage to adding it, and it depends on
immintrin.h which was added in gcc 4.4, so it breaks with older
host compilers.

For details, see:

http://trac.enlightenment.org/e/ticket/942



Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>