Auto merge of #136225 - fmease:rollup-fm7m744, r=fmease

Rollup of 7 pull requests

Successful merges:

 - #135625 ([cfg_match] Document the use of expressions.)
 - #135902 (Do not consider child bound assumptions for rigid alias)
 - #135943 (Rename `Piece::String` to `Piece::Lit`)
 - #136104 (Add mermaid graphs of NLL regions and SCCs to polonius MIR dump)
 - #136143 (Update books)
 - #136147 (ABI-required target features: warn when they are missing in base CPU)
 - #136164 (Refactor FnKind variant to hold &Fn)

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

Author: bors

tests/pass/shims/x86/intrinsics-x86-pause-without-sse2.rs

@@ -1,5 +1,5 @@
-// We're testing x86 target specific features
-//@only-target: x86_64 i686
+// We're testing x86-32 target specific features. SSE always exists on x86-64.
+//@only-target: i686
 //@compile-flags: -C target-feature=-sse2
 
 #[cfg(target_arch = "x86")]