rustc_resolve: fix instability in lib.rmeta contents

rust-lang/rust@23032f31c9 accidentally introduced some nondeterminism
in the ordering of lib.rmeta files, which we caught in our bazel-based
builds only recently due to being further behind than normal. In my
testing, this fixes the issue.

Cargo.lock

@@ -4316,6 +4316,7 @@ name = "rustc_resolve"
 version = "0.0.0"
 dependencies = [
  "bitflags",
+ "itertools",
  "pulldown-cmark 0.11.3",
  "rustc_arena",
  "rustc_ast",

compiler/rustc_resolve/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
+itertools = "0.12"
 pulldown-cmark = { version = "0.11", features = ["html"], default-features = false }
 rustc_arena = { path = "../rustc_arena" }
 rustc_ast = { path = "../rustc_ast" }

compiler/rustc_resolve/src/rustdoc.rs

@@ -1,6 +1,7 @@
 use std::mem;
 use std::ops::Range;
 
+use itertools::Itertools;
 use pulldown_cmark::{
     BrokenLink, BrokenLinkCallback, CowStr, Event, LinkType, Options, Parser, Tag,
 };
@@ -454,7 +455,7 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
         }
     }
 
-    for (label, refdef) in event_iter.reference_definitions().iter() {
+    for (label, refdef) in event_iter.reference_definitions().iter().sorted_by_key(|x| x.0) {
         if !refids.contains(label) {
             links.push(preprocess_link(&refdef.dest));
         }