Rollup merge of #116284 - RalfJung:no-nan-match, r=cjgillot

make matching on NaN a hard error, and remove the rest of illegal_floating_point_literal_pattern

These arms would never be hit anyway, so the pattern makes little sense. We have had a future-compat lint against float matches in general for a *long* time, so I hope we can get away with immediately making this a hard error.

This is part of implementing https://github.com/rust-lang/rfcs/pull/3535.

Closes https://github.com/rust-lang/rust/issues/41620 by removing the lint.

https://github.com/rust-lang/reference/pull/1456 updates the reference to match.

compiler/rustc_lint/src/lib.rs

@@ -516,6 +516,10 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, see PR #118649 \
          <https://github.com/rust-lang/rust/pull/118649> for more information",
     );
+    store.register_removed(
+        "illegal_floating_point_literal_pattern",
+        "no longer a warning, float patterns behave the same as `==`",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {