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

[Aleksey Shipilev]

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

For me, there is a huge question on portable JDK builds, which are usually built with the lowest GCC toolchain possible to avoid GLIBC incompatibilities. I am pretty sure currently built portable builds are _not_ riding as high as GCC 10. 

Looks like the majority of C++17 features were implemented in GCC 6 and GCC 7: https://gcc.gnu.org/projects/cxx-status.html#cxx17, and how Kim mentions, C++17 is no longer experimental for GCC 9. So maybe we should not rush GCC 10, and at most have GCC 9 as minimum.

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PR Comment: https://git.openjdk.org/jdk/pull/14988#issuecomment-1895729165