Changes

x86-64: Use rep movs instructions if array copy size greater than 32 bytes

This change applies to byte and char array System.arraycopy
sequence. It avoids using vector instructions for copy
size between 32 bytes to 64 bytes due to an observed regression.

Signed-off-by: Annabelle Huo <Annabelle.Huo@ibm.com>
 (commit: 8aa9487)