Do not clone Arc when hashing span.

compiler/rustc_span/src/lib.rs

@@ -2600,7 +2600,7 @@ pub trait HashStableContext {
     fn span_data_to_lines_and_cols(
         &mut self,
         span: &SpanData,
-    ) -> Option<(Arc<SourceFile>, usize, BytePos, usize, BytePos)>;
+    ) -> Option<(StableSourceFileId, usize, BytePos, usize, BytePos)>;
     fn hashing_controls(&self) -> HashingControls;
 }
 
@@ -2657,7 +2657,7 @@ where
         };
 
         Hash::hash(&TAG_VALID_SPAN, hasher);
-        Hash::hash(&file.stable_id, hasher);
+        Hash::hash(&file, hasher);
 
         // Hash both the length and the end location (line/column) of a span. If we
         // hash only the length, for example, then two otherwise equal spans with