RFR: 8314488: Compile the JDK as C++17 [v6]

[Kim Barrett]

On Thu, 11 Jan 2024 13:23:45 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> Compile the JDK as C++17, enabling the use of all C++17 language features
>
> Julian Waters has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Require clang 13 in toolchain.m4

As I said earlier, I think the change to build with C++17 needs motivation, probably in the form of proposed changes
to the style guide to describe new features whose use is permitted (or forbidden!) in HotSpot.  There is also
non-HotSpot C++ code in the JDK, and buy-in from the relevant teams will also be needed for that, or decide to
limit the scope of the change.  (I'm not really a fan of that, but mentioning it as an option.)

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PR Comment: https://git.openjdk.org/jdk/pull/14988#issuecomment-1997122909