RFR: 8358693: [leyden] Bootstrapping circularity leads to never starting preload threads

[Vladimir Kozlov]

On Thu, 5 Jun 2025 12:33:00 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> This relates to [JDK-8358690](https://bugs.openjdk.org/browse/JDK-8358690), but we want to make sure Leyden preload runs until we have a fuller fix.
> 
> Additional testing:
>  - [x] Ad-hoc perf tests
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`

Please update `AOTCodeCache::is_code_load_thread_on()` instead.

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PR Review: https://git.openjdk.org/leyden/pull/75#pullrequestreview-2900942432