Xcode: Add function to conditionally add Xcode Attributes

Source/cmXCodeObject.h

@@ -62,6 +62,8 @@ public:
   Type GetType() const { return this->TypeValue; }
   PBXType GetIsA() const { return this->IsA; }
 
+  bool IsEmpty() const;
+
   void SetString(const std::string& s);
   const std::string& GetString() const { return this->String; }
 
@@ -70,6 +72,13 @@ public:
     this->ObjectAttributes[name] = value;
   }
 
+  void AddAttributeIfNotEmpty(const std::string& name, cmXCodeObject* value)
+  {
+    if (value && !value->IsEmpty()) {
+      AddAttribute(name, value);
+    }
+  }
+
   void SetObject(cmXCodeObject* value) { this->Object = value; }
   cmXCodeObject* GetObject() { return this->Object; }
   void AddObject(cmXCodeObject* value) { this->List.push_back(value); }