RFR: Reuse MacroAssembler-CAS-Obj for C1. Plus some minor/cosmetic changes in cas-obj code

[Roman Kennke]

This makes C1 reuse the CAS-Obj impl of MacroAssembler.
It also changes the cas-obj impl so that it uses movl for compressed
oops, and use Assembler::equal instead of ::zero for the final set
instruction, just to be consistent with the other comparisons in that
code. Should be cosmetic afaict.

http://cr.openjdk.java.net/~rkennke/c1casobj/webrev.00/

Ok?
Roman