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_middle/src/middle/region.rs

@@ -149,6 +149,7 @@ rustc_index::newtype_index! {
     ///   and thus does not include EXPR_2, but covers the `...`.
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     pub struct FirstStatementIndex {}
 }
 

compiler/rustc_middle/src/mir/coverage.rs

@@ -18,6 +18,7 @@ rustc_index::newtype_index! {
     /// to use a larger representation on the Rust side.
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     #[max = 0xFFFF_FFFF]
     #[debug_format = "CounterId({})"]
     pub struct CounterId {}
@@ -39,6 +40,7 @@ rustc_index::newtype_index! {
     /// to use a larger representation on the Rust side.
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     #[max = 0xFFFF_FFFF]
     #[debug_format = "ExpressionId({})"]
     pub struct ExpressionId {}

compiler/rustc_middle/src/mir/mod.rs

@@ -737,6 +737,7 @@ impl SourceInfo {
 rustc_index::newtype_index! {
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     #[debug_format = "_{}"]
     pub struct Local {
         const RETURN_PLACE = 0;
@@ -1173,6 +1174,7 @@ rustc_index::newtype_index! {
     /// [guide-mir]: https://rustc-dev-guide.rust-lang.org/mir/
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     #[debug_format = "bb{}"]
     pub struct BasicBlock {
         const START_BLOCK = 0;
@@ -1537,6 +1539,7 @@ impl UserTypeProjection {
 rustc_index::newtype_index! {
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     #[debug_format = "promoted[{}]"]
     pub struct Promoted {}
 }

compiler/rustc_middle/src/ty/sty.rs

@@ -1613,6 +1613,7 @@ rustc_index::newtype_index! {
     /// A **region** (lifetime) **v**ariable **ID**.
     #[derive(HashStable)]
     #[encodable]
+    #[orderable]
     #[debug_format = "'?{}"]
     pub struct RegionVid {}
 }