rustfmt formats different arms of the same match inconsistently

The big rustc format made some code I care about much less readable. Here's an example:

-            ref mut local @ LocalValue::Live(Operand::Immediate(_)) |
-            ref mut local @ LocalValue::Uninitialized => {
-                Ok(Ok(local))
-            }
+            ref mut local @ LocalValue::Live(Operand::Immediate(_))
+            | ref mut local @ LocalValue::Uninitialized => Ok(Ok(local)),

The actual code running here for this branch got moved onto the same line as the last line of a pattern. That makes it quite hard to visually identify this code -- compared to the old version of the code, the visual separation of pattern and code got lost.

Begin by reproducing the match-arm example from the issue and inspect rustfmt's handling of patterns, arms, and inline bodies. Compare the output with the desired formatting shown in the diff; done means the pattern and arm body remain visually distinct without regressing other match formatting.