git: openjdk/jdk-sandbox: shen-late-barriers: Fix and simplify x86_64 CAS barrier, now passes TestReferenceCAS stress tests

[duke]

Changeset: a4d5f6ac
Branch: shen-late-barriers
Author:    Aleksey Shipilev <aleksey at shipilev.net>
Date:      2025-11-25 13:56:25 +0000
URL:       https://git.openjdk.org/jdk-sandbox/commit/a4d5f6ac991902ec0b21ff2da313fada0722a325

Fix and simplify x86_64 CAS barrier, now passes TestReferenceCAS stress tests

! src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp
! src/hotspot/cpu/x86/gc/shenandoah/shenandoah_x86_64.ad
! src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
! src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.hpp