RFR: 8332744: [REDO] 'internal proprietary API' diagnostics if --system is configured to an earlier JDK version

[Liam Miller-Cushon]

On Fri, 24 May 2024 15:32:09 GMT, Liam Miller-Cushon <cushon at openjdk.org> wrote:

> This change fixes a bug preventing javac from emitting 'compiler.warn.sun.proprietary' diagnostics if `--system` is set to a non-default value. The diagnostics are currently emitted for values of `--release`, and for the default value of `--system`.
> 
> The is a redo of [JDK-8331081](https://bugs.openjdk.org/browse/JDK-8331081), which was backed out in [JDK-8332740](https://bugs.openjdk.org/browse/JDK-8332740) due to a build failure in the microbenchmarks.

I still think it'd be slightly worthwhile to fix the built-in sunapi implementation to handle this case, but if the feeling is that it isn't worth spending time on and the possible disruption to `-Werror`, that's also OK.

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PR Comment: https://git.openjdk.org/jdk/pull/19397#issuecomment-2274455669