RFR: 8314488: Compiling the JDK with C++17

[Julian Waters]

On Thu, 21 Aug 2025 14:47:14 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to use C++17 for building C++ parts of the JDK. In
> particular this affects HotSpot. This change also includes an update to the
> HotSpot Style Guide regarding C++17 features and their use in HotSpot code.
> 
> Testing: mach5 tier1-8
> 
> This change includes a modification of the Style Guide. Rough consensus among
> the HotSpot Group members is required to make such a change. Only Group
> members should vote for approval (via the github PR), though reasoned
> objections or comments from anyone will be considered. A decision on this
> proposal will not be made before Friday 5-September-2025 at 12h00 UTC.
> 
> Since we're piggybacking on github PRs here, please use the PR review process
> to approve (click on Review Changes > Approve), rather than sending a "vote:
> yes" email reply that would be normal for a CFV.

There's a "CXXFLAGS := -std=c++17" in java.base Lib.gmk that's also no longer needed once the switch to C++17 is made (See https://github.com/openjdk/jdk/pull/14988/files)

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PR Comment: https://git.openjdk.org/jdk/pull/26884#issuecomment-3211074096