RFR: Use imulptr/addptr in MacroAssembler matrix update

[Roman Kennke]

Am 20.03.2017 um 18:28 schrieb Aleksey Shipilev:
> This fixes build failure on i586, even though we never visit this code in i586
> binary:
>   http://cr.openjdk.java.net/~shade/shenandoah/build/masm-matrix-ptr/webrev.01/
>
> In x86_64, imulptr/addptr alias to the same imulq/addq we have now.
>
> Testing: hotspot_gc_shenandoah
>
> Thanks,
> -Aleksey
>
Yes