RFR: 8307907: [ppc] Remove RTM locking implementation [v2]

[Martin Doerr]

On Fri, 9 Jun 2023 18:25:30 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> This PR removes RTM code for PPC64. The instructions are not supported by Power10 processors.
>> The situation is even worse in Power9 compatibility mode on Power10. The VM detects RTM to be available, but the processor is unable to complete any transaction successfully.
>> The feature had so many problems and we never supported it in production.
>
> Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove RTM from feature string. Otherwise, tests complain about it.

Thanks for the reviews! The flags were copied from x86, but they are officially only supported on x86: "Options related to RTM are available only for the Java HotSpot Server VM on x86 CPUs that support Transactional Synchronization Extensions (TSX)." [https://docs.oracle.com/en/java/javase/11/tools/java.html#GUID-3B1CE181-CD30-4178-9602-230B800D4FAE]

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PR Comment: https://git.openjdk.org/jdk/pull/14398#issuecomment-1589484777