RFR: 8372240: Convert FreeListAllocator to use Atomic<T>

[Thomas Schatzl]

On Fri, 21 Nov 2025 09:09:03 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to FreeListAllocator to use Atomic rather than
> directly applying AtomicAccess to volatile members.
> 
> Testing: mach5 tier1-5

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/28447#pullrequestreview-3491888129