…as-schievink

Rollup of 12 pull requests

Successful merges:

 - rust-lang#77037 (more tiny clippy cleanups)
 - rust-lang#77233 (BTreeMap: keep an eye out on the size of the main components)
 - rust-lang#77280 (Ensure that all LLVM components requested by tests are available on CI)
 - rust-lang#77284 (library: Forward compiler-builtins "mem" feature)
 - rust-lang#77296 (liveness: Use Option::None to represent absent live nodes)
 - rust-lang#77322 (Add unstable book docs for `-Zunsound-mir-opts`)
 - rust-lang#77328 (Use `rtassert!` instead of `assert!` from the child process after fork() in std::sys::unix::process::Command::spawn())
 - rust-lang#77331 (Add test for async/await combined with const-generics.)
 - rust-lang#77338 (Fix typo in alloc vec comment)
 - rust-lang#77340 (Alloc vec use imported path)
 - rust-lang#77345 (Add test for issue rust-lang#74761)
 - rust-lang#77348 (Update books)

Failed merges:

r? `@ghost`