Rollup merge of #69561 - JohnTitor:clean-up-unstable-book, r=Mark-Simulacrum

Clean up unstable book

- #58402's feature was renamed to `tidy_test_never_used_anywhere_else` and it is now used for tidy only
- `read_initializer` link is wrong and the doc should be auto-generated so removed
- Add dummy doc for `link_cfg`
- Stop generating `compiler_builtins_lib` doc in favor of b8ccc0f8a6
- Make `rustc_attrs` tracking issue "None"

src/test/ui/consts/min_const_fn/allow_const_fn_ptr_feature_gate.stderr

@@ -4,7 +4,6 @@ error[E0658]: internal implementation detail
 LL | #[rustc_allow_const_fn_ptr]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: aborting due to previous error

src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr

@@ -4,7 +4,6 @@ error[E0658]: the `#[rustc_variance]` attribute is just used for rustc unit test
 LL | #[rustc_variance]
    | ^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error[E0658]: the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
@@ -13,7 +12,6 @@ error[E0658]: the `#[rustc_error]` attribute is just used for rustc unit tests a
 LL | #[rustc_error]
    | ^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error[E0658]: the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and will never be stable
@@ -22,7 +20,6 @@ error[E0658]: the `#[rustc_nonnull_optimization_guaranteed]` attribute is just u
 LL | #[rustc_nonnull_optimization_guaranteed]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: aborting due to 3 previous errors

src/test/ui/feature-gates/feature-gate-rustc-attrs.stderr

@@ -4,7 +4,6 @@ error[E0658]: attributes starting with `rustc` are reserved for use by the `rust
 LL | #[rustc::unknown]
    |   ^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: expected attribute, found macro `rustc::unknown`
@@ -19,7 +18,6 @@ error[E0658]: attributes starting with `rustc` are reserved for use by the `rust
 LL | #[unknown::rustc]
    |            ^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: expected attribute, found macro `unknown::rustc`
@@ -34,7 +32,6 @@ error[E0658]: attributes starting with `rustc` are reserved for use by the `rust
 LL | #[rustc_unknown]
    |   ^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: cannot find attribute `rustc_unknown` in this scope
@@ -49,7 +46,6 @@ error[E0658]: the `#[rustc_dummy]` attribute is just used for rustc unit tests a
 LL | #[rustc_dummy]
    | ^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: aborting due to 7 previous errors

src/test/ui/on-unimplemented/feature-gate-on-unimplemented.stderr

@@ -4,7 +4,6 @@ error[E0658]: this is an internal attribute that will never be stable
 LL | #[rustc_on_unimplemented = "test error `{Self}` with `{Bar}`"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: aborting due to previous error

src/test/ui/proc-macro/expand-to-unstable-2.stderr

@@ -4,7 +4,6 @@ error[E0658]: attributes starting with `rustc` are reserved for use by the `rust
 LL | #[derive(Unstable)]
    |          ^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
    = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/reserved/reserved-attr-on-macro.stderr

@@ -4,7 +4,6 @@ error[E0658]: attributes starting with `rustc` are reserved for use by the `rust
 LL | #[rustc_attribute_should_be_reserved]
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: cannot determine resolution for the macro `foo`

src/test/ui/suggestions/attribute-typos.stderr

@@ -4,7 +4,6 @@ error[E0658]: attributes starting with `rustc` are reserved for use by the `rust
 LL | #[rustc_err]
    |   ^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: cannot find attribute `rustc_err` in this scope

src/test/ui/tool-attributes/diagnostic_item.stderr

@@ -4,7 +4,6 @@ error[E0658]: diagnostic items compiler internal support for linting
 LL | #[rustc_diagnostic_item = "foomp"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
 error: aborting due to previous error