[llvm] [IR][AtomicExpand] Add elementwise modifier to atomicrmw; automatically expand for all targets (PR #189517)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,8 @@
+; RUN: not llvm-as -disable-output %s -o /dev/null 2>&1 | FileCheck %s
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arsenm wrote:

```suggestion
; RUN: not llvm-as -disable-output %s 2>&1 | FileCheck %s
```

https://github.com/llvm/llvm-project/pull/189517