RFR: 8353009: Document target selection flag for Windows AArch64 builds

[Erik Joelsson]

On Mon, 31 Mar 2025 15:00:08 GMT, Saint Wesonga <duke at openjdk.org> wrote:

> > > Wait, are you saying you can get a native build to work by setting --build=aarch64-pc-cygwin? If so, then that's a better instruction IMO.
> > 
> > 
> > No, it's not. If we could block the `--build` flag, we would. This is the built-in autoconf target/host/build system, that messes with the structure we use in OpenJDK (since we do not do canadian cross builds).
> > So if you need to add configure option, this would be the correct one.
> > However, we should be able to figure this out by ourselves. This can be solved by a patch in `config.sub` and/or `config.guess`.
> 
> Thanks for the clarification that the --build flag is undesirable

I do not agree with `--build` being undesirable in this specific instance. I agree that it's generally not a flag we want to encourage using, but in this specific case, it's necessary to perform a native build on this platform.

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PR Comment: https://git.openjdk.org/jdk/pull/24267#issuecomment-2766916854