[lldb] Override GetVariable in ValueObjectSynthetic (NFC)

[kastiglione]

Summary

Make GetVariable a passthrough function the the underlying value object in ValueObjectSynthetic.

[kastiglione]

Jim approved offline.

lldb/include/lldb/Core/ValueObjectSyntheticFilter.h

lldb::ValueObjectSP GetStaticValue() override {
     return ((m_parent != nullptr) ? m_parent->GetStaticValue() : GetSP());
   }
 
   virtual lldb::DynamicValueType GetDynamicValueType() {
     return ((m_parent != nullptr) ? m_parent->GetDynamicValueType()
                                   : lldb::eNoDynamicValues);
   }
 
+  lldb::VariableSP GetVariable() override {
+    return m_parent != nullptr ? m_parent->GetVariable() : nullptr;
+  }
+
   ValueObject *GetParent() override {
     return ((m_parent != nullptr) ? m_parent->GetParent() : nullptr);
   }
 
   const ValueObject *GetParent() const override {
     return ((m_parent != nullptr) ? m_parent->GetParent() : nullptr);
   }