DebugInfo: Rebuild varargs function types correctly

Improves llvm-dwarfdump output and for simplified template names roundtripping.

Author: dwblaikie

cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.cpp

@@ -217,6 +217,8 @@ int main() {
   f1<decltype(L)>();
   t3<decltype(L)> v1;
   f1<int(float)>();
+  f1<void(...)>();
+  f1<void(int, ...)>();
   f1<const int &>();
   f1<const int *&>();
   f1<t5>();

llvm/lib/DebugInfo/DWARF/DWARFDie.cpp

@@ -611,7 +611,8 @@ struct DWARFTypePrinter {
     bool First = true;
     bool RealFirst = true;
     for (DWARFDie P : D) {
-      if (P.getTag() != DW_TAG_formal_parameter)
+      if (P.getTag() != DW_TAG_formal_parameter &&
+          P.getTag() != DW_TAG_unspecified_parameters)
         return;
       DWARFDie T = resolveReferencedType(P);
       if (SkipFirstParamIfArtificial && RealFirst && P.find(DW_AT_artificial)) {
@@ -623,7 +624,10 @@ struct DWARFTypePrinter {
         OS << ", ";
       }
       First = false;
-      appendQualifiedName(T);
+      if (P.getTag() == DW_TAG_unspecified_parameters)
+        OS << "...";
+      else
+        appendQualifiedName(T);
     }
     EndedWithTemplate = false;
     OS << ')';