[clang] [AMDGPU] add function attrbute amdgpu-lib-fun (PR #74737)

[Joseph Huber via cfe-commits]

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@@ -2011,6 +2011,13 @@ def AMDGPUNumVGPR : InheritableAttr {
   let Subjects = SubjectList<[Function], ErrorDiag, "kernel functions">;
 }
 
+def AMDGPULibFun : InheritableAttr {
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jhuber6 wrote:

Why isn't this a `TargetSpecificAttr`? We should have one for AMDGPU.

https://github.com/llvm/llvm-project/pull/74737