RFR: 8187520: Add --disable-javac-warnings-as-errors configure option

[Magnus Ihse Bursie]

On Mon, 7 Apr 2025 11:11:08 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> Analogous with how native warnings can be treated as errors or not using the `--disable-warnings-as-errors` configure flag, this patch introduces a `--disable-javac-warnings-as-errors` flag.
> 
> The reason that this is not made part of `--disable-warnings-as-errors` is discussed in the JBS issue, but in short, native warnings can easily occur due to different build environment or compiler versions, while javac warnings are platform independent and should only depend on the source code we compile. That means that this option is basically only needed by developers to temporary silence javac while developing new code.

Note that this PR removes the undocumented method of setting `JAVA_WARNINGS_ARE_ERRORS` on the command line. Since this was never documented nor very well-known by developers, I don't see a need to make any transition arrangements.

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PR Comment: https://git.openjdk.org/jdk/pull/24486#issuecomment-2782966210