RFR: 8332082: Shenandoah: Use SATB active flag for C2 pre-write barrier on x86 and PPC

[William Kemper]

On Fri, 10 May 2024 16:13:51 GMT, William Kemper <wkemper at openjdk.org> wrote:

> This is consistent with c1 and other platforms.

`ShenandoahBarrierSetC2::verify_gc_barriers` is also looking for IR node pattern for `SATBMarkQueue.isActive`, so it'll need rework too.

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PR Comment: https://git.openjdk.org/jdk/pull/19180#issuecomment-2113004499