RFR: 8286476: x86_32: Fix crashes with non-preview mode after JDK-8284161 (Virtual Threads) [v4]

[Aleksey Shipilev]

On Tue, 10 May 2022 15:29:40 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Virtual Threads are not fully implemented on x86_32. The feature is guarded with `--enable-preview`. But there is some VM code that is executed unconditionally anyway, crashing the VM on some tests. This improves the x86_32 code to the point that tests without `--enable-preview` run successfully. This adds the scaffolding for full implementation too. 
>> 
>> Additional testing:
>>  - [x] Linux x86_32 fastdebug, `tier1` failures only with `--enable-preview`
>>  - [x] Linux x86_32 fastdebug, `tier2` failures only with `--enable-preview`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Rebasing after JDK-8286480
>  - Merge branch 'master' into JDK-8286476-loom-x86-32-no-preview
>  - x86-64 code still a bit wrong
>  - Fix x86_64 release build
>  - Fallback for 32-bit port signature helpers
>  - Fix jdk_jfr

I merged from master to check there are no conflicts with PPC64 code. Looks fine on x86_32 side.

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PR: https://git.openjdk.java.net/jdk/pull/8630