RFR: 8292591: Experimentally add back barrier-less Java thread transitions [v2]

[Robbin Ehn]

On Thu, 8 Sep 2022 09:44:44 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Please consider, only implemented on x64/aarch64 linux/windows.
>> 
>> On my box calling clock_gettime via JNI goes from 35ns to 28ns when enabled.
>> 
>> Passes t1-7 with option forced on, also passes t1-4 as is in this PR.
>
> Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Change header and constants handling

There is problem using AC_CHECK_DECL during cross-compiles, so I had to remove that until that is fixed.
For now the enum value is hardcoded, it is the same on all platforms.

Regarding the defines, it seems like it's only us that needs it for some x64 builds.
If someone else needs it, they can just add it. Since that you not really happen, I this approach is fine? 

So now the membarrier is working on all Linux platforms. (but obviously local membarrier must be conditioned for any performance benefits)

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PR: https://git.openjdk.org/jdk/pull/10123