RFR: In ASM SATB barrier, mov pre_val to c_rarg0 before call early, to protect c_rarg1

[Aleksey Shipilev]

On 06/20/2018 02:45 PM, Roman Kennke wrote:
> http://cr.openjdk.java.net/~rkennke/c1-satb-regs/webrev.00/

I verified with VerifyJCStress in my failing workload -- it passes.

Minor nit: "smarged"?
  266   assert(thread != c_rarg0, "smarged arg");

Otherwise good, thanks for fixing this!

-Aleksey