Auto merge of #123165 - oli-obk:no_ord_def_id3, r=cjgillot

Stop sorting `Span`s' `SyntaxContext`, as that is incompatible with incremental

work towards https://github.com/rust-lang/rust/issues/90317

Luckily no one actually needed these to be sorted, so it didn't even affect diagnostics. I'm guessing they'd have been sorted by creation time anyway, so it wouldn't really have mattered.

r? `@cjgillot`

compiler/rustc_span/src/hygiene.rs

@@ -43,9 +43,15 @@ use std::hash::Hash;
 use tracing::{debug, trace};
 
 /// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct SyntaxContext(u32);
 
+// To ensure correctness of incremental compilation,
+// `SyntaxContext` must not implement `Ord` or `PartialOrd`.
+// See https://github.com/rust-lang/rust/issues/90317.
+impl !Ord for SyntaxContext {}
+impl !PartialOrd for SyntaxContext {}
+
 #[derive(Debug, Encodable, Decodable, Clone)]
 pub struct SyntaxContextData {
     outer_expn: ExpnId,