F401 use BTreeMap instead of FxHashMap (#11621)

* Potentially resolves #11619 (nondeterministic hashmap order across
different architectures) in F401 by replacing a hashmap with
nondeterministic traversal order with an ordered mapping.

I'm not sure how to test this with our CI/CD. I don't have an s390x
machine at home. Should I try it in Qemu?

crates/ruff_linter/src/rules/pyflakes/rules/unused_import.rs

@@ -2,7 +2,7 @@ use std::borrow::Cow;
 use std::iter;
 
 use anyhow::{anyhow, bail, Result};
-use rustc_hash::FxHashMap;
+use std::collections::BTreeMap;
 
 use ruff_diagnostics::{Applicability, Diagnostic, Fix, FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, violation};
@@ -220,8 +220,8 @@ fn find_dunder_all_exprs<'a>(semantic: &'a SemanticModel) -> Vec<&'a ast::Expr>
 ///
 pub(crate) fn unused_import(checker: &Checker, scope: &Scope, diagnostics: &mut Vec<Diagnostic>) {
     // Collect all unused imports by statement.
-    let mut unused: FxHashMap<(NodeId, Exceptions), Vec<ImportBinding>> = FxHashMap::default();
-    let mut ignored: FxHashMap<(NodeId, Exceptions), Vec<ImportBinding>> = FxHashMap::default();
+    let mut unused: BTreeMap<(NodeId, Exceptions), Vec<ImportBinding>> = BTreeMap::default();
+    let mut ignored: BTreeMap<(NodeId, Exceptions), Vec<ImportBinding>> = BTreeMap::default();
 
     for binding_id in scope.binding_ids() {
         let binding = checker.semantic().binding(binding_id);

crates/ruff_python_semantic/src/binding.rs

@@ -565,7 +565,7 @@ pub enum BindingKind<'a> {
 }
 
 bitflags! {
-    #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+    #[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
     pub struct Exceptions: u8 {
         const NAME_ERROR = 0b0000_0001;
         const MODULE_NOT_FOUND_ERROR = 0b0000_0010;