[llvm] [AMDGPU] Add verification for amdgcn.init.exec.from.input (PR #128172)

[Matt Arsenault via llvm-commits]

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@@ -1,5 +1,4 @@
-; RUN: sed -e '/^; MARK$/,$d' %s | not llc -mtriple=amdgcn -mcpu=gfx942 2>&1 | FileCheck %s
-; RUN: sed -e '1,/^; MARK$/d' %s | llc -mtriple=amdgcn -mcpu=gfx942 -filetype=null
+; RUN: not llvm-as -o /dev/null 2>&1 %s | FileCheck %s
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arsenm wrote:

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

https://github.com/llvm/llvm-project/pull/128172