Link for source of is_x86_feature_detected is broken

[hellow554]

IIRC there is a broken link checker, but somehow it doesn't catch this case:

https://doc.rust-lang.org/std/macro.is_x86_feature_detected.html

https://doc.rust-lang.org/1.60.0/src/std_detect/detect/arch/x86.rs.html#18-197 which is a 404

@rustbot modify labels: A-docs

[hellow554]

Also, all source links of the macros in https://doc.rust-lang.org/nightly/std/arch/index.html are broken as well.

[GuillaumeGomez]

Another reexport bug. :)

EDIT: so in here the problem is that the std_detect crate isn't documented on doc.rust-lang.org. It should redirect to docs.rs.

[jyn514]

I think the right fix is to pass -Zrustdoc-map to cargo when documenting the standard library. We already do that for the compiler docs:

rust/src/bootstrap/doc.rs

Line 698 in 96834f0

cargo.arg("-Zrustdoc-map");

mentoring instructions: add that same flag to impl Step for doc::Std.

[jyn514]

cc #81311, which is one way to fix this in rustdoc, but will result in a worse experience for the source view.