[llvm] Add diagnostic help for inline asm operand constraint 'H' (PR #86910)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,9 @@
+; RUN: not llc -march x86 < %s 2> %t
+; RUN: FileCheck %s < %t
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arsenm wrote:

Don't use a temporary file
```suggestion
; RUN: not llc -march x86 < %s 2>&1 | FileCheck %s
```

https://github.com/llvm/llvm-project/pull/86910