RFR: 8372393: Document requirement for separate metallib installation with Xcode 26.1.1

[Galder Zamarreño]

On Tue, 25 Nov 2025 13:56:34 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> Document the metal toolchain requirements starting with Xcode 26.
>
> doc/building.html line 547:
> 
>> 545: comes bundled with Xcode, so it needs to be installed separately. This can
>> 546: either be done via the Xcode's Settings/Components UI, or in the command line
>> 547: calling <code>xcodebuild -downloadComponent metalToolchain</code>.</p>
> 
> When I checkout this branch and run `make update-build-docs`, the line breaks here are done differently. It would be good to not introduce future diffs when the html files are regenerated next time.
> 
> Suggestion:
> 
> <p>Starting with Xcode 26, introduced in macOS 26, the Metal toolchain
> no longer comes bundled with Xcode, so it needs to be installed
> separately. This can either be done via the Xcode's Settings/Components
> UI, or in the command line calling
> <code>xcodebuild -downloadComponent metalToolchain</code>.</p>

Aha, I was not aware of that make target. I'll execute and update

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PR Review Comment: https://git.openjdk.org/jdk/pull/28489#discussion_r2568012748