rel-notes: Note backport of #22010

docs/users_guide/9.8.4-notes.rst

@@ -18,6 +18,8 @@ Compiler
   have expose the same module name (:ghc-ticket:`25122`).
 - Adjust the demand signature of the ``prompt#`` to avoid invalid optimisation of
   non-terminating programs (:ghc-ticket:`25439`).
+- GHC's internal ``Unique`` type has been widened to 64-bits on 32-bit architectures, avoiding
+  potential miscompilations on large projects (:ghc-ticket:`22010`).
 
 Packaging
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