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

[Kim Barrett]

On Fri, 12 Jan 2024 07:49:17 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> We at SAP use and document xlC 17.1.1.4 for jdk22 (use the same for jdk23) https://wiki.openjdk.org/display/Build/Supported+Build+Platforms
> 
> version 17.1.1.4 is already clang15 (at least that's what the compiler output is telling me)
> 
> /opt/IBM/openxlC/17.1.1/bin/ibm-clang++_r -v IBM Open XL C/C++ for AIX 17.1.1 (5725-C72, 5765-J18), version 17.1.1.4, clang version 15.0.0 (build ca7115e) Target: powerpc-ibm-aix7.2.0.0

My mistake, you are correct.  17.1.0 seems to be clang 13, 17.1.1 seems to be clang 15, and 17.1.2 seems to be clang 17.
All of those are based on the documented value of the `__VERSION__` macro's string value.

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PR Comment: https://git.openjdk.org/jdk/pull/14988#issuecomment-1888731423