Rollup merge of #139797 - folkertdev:naked-allow-unsafe, r=tgross35
Allow (but don't require) `#[unsafe(naked)]` so that `compiler-builtins` can upgrade to it
tracking issue: https://github.com/rust-lang/rust/issues/138997
Per https://github.com/rust-lang/rust/pull/134213#issuecomment-2755984503, we want to make the `#[naked]` attribute an unsafe attribute. Making that change runs into a cyclic dependency with `compiler-builtins` which uses `#[naked]`, where `rustc` needs an updated `compiler-builtins` and vice versa.
So based on https://github.com/rust-lang/rust/pull/139753 and [#t-compiler/help > updating `compiler-builtins` and `rustc`](https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/updating.20.60compiler-builtins.60.20and.20.60rustc.60), this PR allows, but does not require `#[unsafe(naked)]`, and makes that change for some of the tests to check that both `#[naked]` and `#[unsafe(naked)]` are accepted.
Then we can upgrade and synchronize `compiler-builtins`, and then make `#[naked]` (without `unsafe`) invalid.
r? `@traviscross` (or someone from t-compiler if you're faster and this look allright)
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