test: select memcpy alignment unit at run-time
test: select memcpy alignment unit at run-time

This patch modifies assignment of alignment unit from build-time
to run-time based on CPU flags that machine supports.

Signed-off-by: Xiaoyun Li <151cc00bdba86cfa2ecfc39aaa98def8f092d9d8@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk