[llvm] [DirectX] Strip `dx.rootsignatures` metadata during `dxil-prepare` (PR #145746)

[Justin Bogner via llvm-commits]

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@@ -0,0 +1,17 @@
+; RUN: opt -S -dxil-prepare < %s | FileCheck %s
+
+; Ensures that dxil-prepare will remove the dx.rootsignatures metadata
+
+target triple = "dxil-unknown-shadermodel6.0-compute"
+
+define void @main() {
+entry:
+  ret void
+}
+
+; CHECK-NOT: !dx.rootsignature
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bogner wrote:

Typo here (though it would still catch the problem). Should we also do a `CHECK-NOT: {{^!}}` or so to make sure the elements are cleaned up too?
```suggestion
; CHECK-NOT: !dx.rootsignatures
; CHECK-NOT: {{^!}}
```

https://github.com/llvm/llvm-project/pull/145746