mk: fix detection of SSE4.2 on FreeBSD

mk: fix detection of SSE4.2 on FreeBSD

Add a special case to the native target makefile, where we check if
-march=native shows SSE4.2 support. If it does not, then not everything may
build, so we check if the hardware supports SSE4.2, and use a corei7 target
explicitly to get the SSE4.2 support.

Then ACL library, which requires SSE4.2, can be re-enabled for FreeBSD.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Zhaochen Zhan <zhaochen.zhan@intel.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>