Replace no_ord_impl with orderable.

Similar to the previous commit, this replaces `newtype_index`'s opt-out
`no_ord_impl` attribute with the opt-in `orderable` attribute.

compiler/rustc_span/src/def_id.rs

@@ -13,6 +13,7 @@ pub type StableCrateIdMap =
     indexmap::IndexMap<StableCrateId, CrateNum, BuildHasherDefault<Unhasher>>;
 
 rustc_index::newtype_index! {
+    #[orderable]
     #[debug_format = "crate{}"]
     pub struct CrateNum {}
 }
@@ -212,6 +213,7 @@ rustc_index::newtype_index! {
     /// A DefIndex is an index into the hir-map for a crate, identifying a
     /// particular definition. It should really be considered an interned
     /// shorthand for a particular DefPath.
+    #[orderable]
     #[debug_format = "DefIndex({})"]
     pub struct DefIndex {
         /// The crate root is always assigned index 0 by the AST Map code,

compiler/rustc_span/src/hygiene.rs

@@ -60,6 +60,7 @@ pub struct SyntaxContextData {
 
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
+    #[orderable]
     pub struct ExpnIndex {}
 }
 
@@ -79,7 +80,6 @@ impl fmt::Debug for ExpnId {
 
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
-    #[no_ord_impl]
     #[debug_format = "expn{}"]
     pub struct LocalExpnId {}
 }

compiler/rustc_span/src/symbol.rs

@@ -2018,6 +2018,7 @@ impl fmt::Display for MacroRulesNormalizedIdent {
 pub struct Symbol(SymbolIndex);
 
 rustc_index::newtype_index! {
+    #[orderable]
     struct SymbolIndex {}
 }