RFR: 8320888: Shenandoah: Enable ShenandoahVerifyOptoBarriers in debug builds

[Roman Kennke]

On Tue, 28 Nov 2023 12:40:41 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Flag cleanup. Current barrier verification code is opt-in, and it is selected for a few tests. For extra safety, we want to have it enabled by default in debug builds. This also simplifies test configurations.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
>  - [x] Linux AArch64 server fastdebug, `hotspot_gc_shenandoah`
>  - [x] Linux x86_64 server fastdebug, `tier{1,2,3,4}` with `-XX:+UseShenandoahGC`
>  - [x] Linux AArch64 server fastdebug, `tier{1,2,3,4}` with `-XX:+UseShenandoahGC`

Makes sense and looks good, thank you!

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Marked as reviewed by rkennke (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16849#pullrequestreview-1755819547