RFR: JDK-8300783: Consolidate byteswap implementations [v5]

[David Holmes]

On Sat, 21 Jan 2023 18:21:26 GMT, Justin King <jcking at openjdk.org> wrote:

>> Deduplicate byte swapping implementations by consolidating them into `utilities/byteswap.hpp`, following `std::byteswap` introduced in C++23. Further simplification of `Bytes` will follow in https://github.com/openjdk/jdk/pull/12078.
>
> Justin King has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add XL C/C++ builtins
>   
>   Signed-off-by: Justin King <jcking at google.com>

Looking like a good cleanup but can we not put the `swap_uN` definitions in `byteswap.hpp` so we don't repeat then for each platform? Thanks.

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Changes requested by dholmes (Reviewer).

PR: https://git.openjdk.org/jdk/pull/12114