Auto merge of #136943 - GuillaumeGomez:rollup-amtd3mq, r=GuillaumeGomez

Rollup of 10 pull requests

Successful merges:

 - #136758 (tests: `-Copt-level=3` instead of `-O` in assembly tests)
 - #136761 (tests: `-Copt-level=3` instead of `-O` in codegen tests)
 - #136784 (Nuke `Buffer` abstraction from `librustdoc`, take 2 💣)
 - #136838 (Check whole `Unsize` predicate for escaping bound vars)
 - #136848 (add docs and ut for bootstrap util cache)
 - #136871 (dev-guide: Link to `t-lang` procedures for new features)
 - #136890 (Change swap_nonoverlapping from lang to library UB)
 - #136901 (compiler: give `ExternAbi` truly stable `Hash` and `Ord`)
 - #136907 (compiler: Make middle errors `pub(crate)` and bury the dead code)
 - #136916 (use cc archiver as default in `cc2ar`)

r? `@ghost`
`@rustbot` modify labels: rollup

src/implementing_new_features.md

@@ -9,7 +9,11 @@ smoothly.
 **NOTE: this section is for *language* features, not *library* features,
 which use [a different process].**
 
+See also [the Rust Language Design Team's procedures][lang-propose] for
+proposing changes to the language.
+
 [a different process]: ./stability.md
+[lang-propose]: https://lang-team.rust-lang.org/how_to/propose.html
 
 ## The @rfcbot FCP process