RFR: 8145717: Use AVX3 instructions for Arrays.equals() intrinsic

[Civlin, Jan]

We would like to contribute AVX3 patch for Arrays.equals() intrinsic.

This utilizes 512 bits registers on AVX3 architecture and delivers performance gain (speed-up):
- on a random (any size) about 10% speed-up;
- on a long (equal or not - randomly) about 25%; 
- on a long equal (it is the longest processing, since all the bytes matter) almost 40% - test time dropped from 12 sec to 7.5 sec.


Contributor: Jan Civlin.


Bug-id: https://bugs.openjdk.java.net/browse/JDK-8145717
Webrev:  http://cr.openjdk.java.net/~kvn/8145717/webrev/