[ItaniumDemangle] Add getter for constructor/destructor variants

This patch adds a way to retrieve the constructor/destructor variant
from the Itanium demangle tree. This will be used by LLDB.

Author: Michael137

libcxxabi/src/demangle/ItaniumDemangle.h

@@ -1766,6 +1766,8 @@ class CtorDtorName final : public Node {
 
   template<typename Fn> void match(Fn F) const { F(Basename, IsDtor, Variant); }
 
+  int getVariant() const { return Variant; }
+
   void printLeft(OutputBuffer &OB) const override {
     if (IsDtor)
       OB += "~";

llvm/include/llvm/Demangle/Demangle.h

@@ -127,6 +127,9 @@ struct ItaniumPartialDemangler {
   /// If this symbol describes a constructor or destructor.
   DEMANGLE_ABI bool isCtorOrDtor() const;
 
+  /// If this symbol describes a constructor or destructor.
+  std::optional<int> getCtorOrDtorVariant() const;
+
   /// If this symbol describes a function.
   DEMANGLE_ABI bool isFunction() const;
 

llvm/include/llvm/Demangle/ItaniumDemangle.h

@@ -1766,6 +1766,8 @@ class CtorDtorName final : public Node {
 
   template<typename Fn> void match(Fn F) const { F(Basename, IsDtor, Variant); }
 
+  int getVariant() const { return Variant; }
+
   void printLeft(OutputBuffer &OB) const override {
     if (IsDtor)
       OB += "~";

llvm/lib/Demangle/ItaniumDemangle.cpp

@@ -560,13 +560,17 @@ bool ItaniumPartialDemangler::hasFunctionQualifiers() const {
 }
 
 bool ItaniumPartialDemangler::isCtorOrDtor() const {
+  return getCtorOrDtorVariant().has_value();
+}
+
+std::optional<int> ItaniumPartialDemangler::getCtorOrDtorVariant() const {
   const Node *N = static_cast<const Node *>(RootNode);
   while (N) {
     switch (N->getKind()) {
     default:
-      return false;
+      return std::nullopt;
     case Node::KCtorDtorName:
-      return true;
+      return static_cast<const CtorDtorName *>(N)->getVariant();
 
     case Node::KAbiTagAttr:
       N = static_cast<const AbiTagAttr *>(N)->Base;
@@ -588,7 +592,7 @@ bool ItaniumPartialDemangler::isCtorOrDtor() const {
       break;
     }
   }
-  return false;
+  return std::nullopt;
 }
 
 bool ItaniumPartialDemangler::isFunction() const {