RFR: 8352914: Shenandoah: Change definition of ShenandoahSharedValue to int32_t to leverage platform atomics

[William Kemper]

On Fri, 5 Dec 2025 18:44:08 GMT, Ben Taylor <btaylor at openjdk.org> wrote:

> The `STATIC_ASSERT` below this typedef appears to be out of date. 
> 
> The barriers check thread local copy of gc state, which is stored in `ShenandoahThreadLocalData::_gc_state`  and is type `char`, so the size requirement described by the assert is maintained even after this change.
> 
> Change passes all tier1 tests locally when run with Shenandoah GC.

Marked as reviewed by wkemper (Reviewer).

This looks good to me, but would appreciate another reviewer.

-------------

PR Review: https://git.openjdk.org/jdk/pull/28681#pullrequestreview-3546051530
PR Comment: https://git.openjdk.org/jdk/pull/28681#issuecomment-3618172121