[clang] [Clang] Fix sema checks thinking kernels aren't kernels (PR #104460)

[Matt Arsenault via cfe-commits]

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@@ -7147,7 +7147,9 @@ void Sema::ProcessDeclAttributeList(
   // good to have a way to specify "these attributes must appear as a group",
   // for these. Additionally, it would be good to have a way to specify "these
   // attribute must never appear as a group" for attributes like cold and hot.
-  if (!D->hasAttr<OpenCLKernelAttr>()) {
+  const FunctionType *FnTy = D->getFunctionType();
+  if (!D->hasAttr<OpenCLKernelAttr>() && FnTy &&
+      FnTy->getCallConv() != CallingConv::CC_AMDGPUKernelCall) {
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arsenm wrote:

Is there no other representation before going straight to the calling conv? Also probably should have an isKernel helper somewhere 

https://github.com/llvm/llvm-project/pull/104460