Update platform support docs for new Windows support policy

[dpaoliello]

rust-lang/compiler-team#651 established that Rust version 1.76+ will only support Windows 10+ as a tier 1 target and introduces new win7 targets for older versions of Windows.

This change updates the platform support docs to reflect that decision, and removes entries for the "Windows XP" targets which appeared to just be the normal Windows targets?

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[dpaoliello]

r? @ChrisDenton

[ChrisDenton]

I also have a PR but that's blocked on having a blog post, which I wrote, but that is blocked on, I think, someone deciding when to publish. It was also decided to push this change back to 1.78 so that there wouldn't be a need to backport documentation.

Good call on the XP thing though. It doesn't really make sense to have it as a tier 3 target when there's no support (though of course no_std can still be made to work).

[dpaoliello]

@ChrisDenton might be worth adding a note to https://blog.rust-lang.org/2023/08/24/Rust-1.72.0.html#future-windows-compatibility to say that the plan has been changed.

Do you want me to keep this PR for Windows XP, or will you merge that into yours?

[ChrisDenton]

It's probably easier if I update my PR rather than having two.

might be worth adding a note to https://blog.rust-lang.org/2023/08/24/Rust-1.72.0.html#future-windows-compatibility to say that the plan has been changed.

I don't know if we usually update old blog posts, cc @wesleywiser

[dpaoliello]

Closing in favor of #115141

[wesleywiser]

It's probably easier if I update my PR rather than having two.

might be worth adding a note to https://blog.rust-lang.org/2023/08/24/Rust-1.72.0.html#future-windows-compatibility to say that the plan has been changed.

I don't know if we usually update old blog posts, cc @wesleywiser

I think updating old blog posts for the purpose of reducing confusion is good, we should just be careful to make it obvious that the post was edited after the fact, rather than always containing the new information.

[ChrisDenton]

I wrote a short update to the original announcement rust-lang/blog.rust-lang.org#1262