Material: fix build failure with Qt6

src/Mod/Material/App/MaterialLibrary.cpp

@@ -81,7 +81,9 @@ Material* MaterialLibrary::saveMaterial(Material& material, const QString& path,
 
     if (file.open(QIODevice::WriteOnly | QIODevice::Text)) {
         QTextStream stream(&file);
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
         stream.setCodec("UTF-8");
+#endif
         stream.setGenerateByteOrderMark(true);
 
         // Write the contents

src/Mod/Material/App/MaterialValue.h

@@ -175,7 +175,20 @@ public:
     const QVariant getValue(int row, int column);
 
 protected:
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
     std::map<QVariant, std::vector<std::vector<QVariant>*>> _rowMap;
+#else
+    struct variant_comp
+    {
+        bool operator()(const QVariant& var1,
+                        const QVariant& var2) const
+        {
+            return QVariant::compare(var1, var2) == QPartialOrdering::Less;
+        }
+    };
+    std::map<QVariant, std::vector<std::vector<QVariant>*>, variant_comp> _rowMap;
+#endif
+
     bool _defaultSet;
 };