[llvm] [BPF] Handle data-carrying enums (PR #155783)

[via llvm-commits]

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@@ -696,10 +710,14 @@ void BTFDebug::visitStructType(const DICompositeType *CTy, bool IsStruct,
   // Visit all struct members.
   int FieldNo = 0;
   for (const auto *Element : Elements) {
-    const auto Elem = cast<DIDerivedType>(Element);
-    visitTypeEntry(Elem);
-    processDeclAnnotations(Elem->getAnnotations(), TypeId, FieldNo);
-    FieldNo++;
+    if (const auto *Elem = dyn_cast<DIDerivedType>(Element)) {
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eddyz87 wrote:

I'd match the tag directly here:
```c++
switch(Elem->getTag()) {
case dwarf::DW_TAG_member: ...
case dwarf::DW_TAG_variant_part: ...
}
```
Also, I'd generate an artificial field for the variant part, if that is possible.

https://github.com/llvm/llvm-project/pull/155783