[vector] Vector compare and miscellaneous cleanup for x86

[Viswanathan, Sandhya]

Please find below a weberv which does the following:

  1.  Merges vector compare instructs where possible
  2.  Removes redundant operands from x86.ad
  3.  Removes SubReduction node

http://cr.openjdk.java.net/~sviswanathan/vectorIntrinsics/CmpCleanup/webrev.00/

Best Regards,
Sandhya