RFR: 8295395: Linux Alpha Zero builds fail after JDK-8292591

[Thomas Stuefe]

On Mon, 17 Oct 2022 07:44:55 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See bug for details. We can just add the fallback definition in the relevant block.
> 
> Additional testing:
>  - [x] Linux Alpha Zero fastdebug build (now passes)

Is membarrier on alpha not 517?

https://github.com/torvalds/linux/blob/master/arch/alpha/kernel/syscalls/syscall.tbl#L448

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PR: https://git.openjdk.org/jdk/pull/10721