Reformat after #2142 (#2149)

Author: Ekdohibs

middle_end/flambda2/simplify/expr_builder.ml

@@ -834,8 +834,8 @@ let rewrite_fixed_arity_apply uacc ~use_id arity apply =
   | _, Never_returns -> make_apply apply
   | None, Return _ ->
     Misc.fatal_errorf
-      "Expr_builder.rewrite_fixed_arity_apply: got no use_id for the return continuation but the apply \
-       could return:@ %a@."
+      "Expr_builder.rewrite_fixed_arity_apply: got no use_id for the return \
+       continuation but the apply could return:@ %a@."
       Apply.print apply
   | Some use_id, Return cont ->
     rewrite_fixed_arity_continuation uacc cont ~use_id arity