RFR: JDK-8306304: Fix xlc17 clang warnings in ppc and aix code [v2]

[JoKern65]

On Thu, 18 May 2023 15:20:22 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Use
>> 
>> struct shmid_ds shm_buf{};
>> 
>> to _value-initialize_.  Calls the default constructor if there is one. Otherwise, performs _zero-initialization_,
>> which is what we want here.
>
> The final suggested change (to direct-value-initialize the object) seems to have *not* been made.
> 
> However, I think it doesn't matter.  The mentioned restriction against being non-empty until C23 is not relevant.
> This is C++, not C.  Empty initializers are, and have always been, permitted by C++.

Strange the last resulting change I see is
`struct shmid_ds shm_buf{};`

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PR Review Comment: https://git.openjdk.org/jdk/pull/13953#discussion_r1200056697