RFR: 8294729: [s390] Implement nmethod entry barriers [v14]

[Martin Doerr]

On Thu, 27 Oct 2022 23:46:43 GMT, Tyler Steele <tsteele at openjdk.org> wrote:

>> This draft PR implements native method barriers on s390. When complete, this will fix the build, and bring the other benefits of [JDK-8290025](https://bugs.openjdk.org/browse/JDK-8290025) to that platform.
>
> Tyler Steele has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Changes
>   
>   - Adds labels to registers used in c2i_entry_barrier
>   - Removes use of R2
>   - Removes erroneous uses of R0
>   - Adds nm->c2i_entry_barrier in gen_i2c2i_adapters

Also, in .hpp file, please.

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PR: https://git.openjdk.org/jdk/pull/10558