qt: Do not use QClipboard::Selection on Windows and macOS.

Windows and macOS do not support the global mouse selection.

src/qt/guiutil.cpp

@@ -628,8 +628,11 @@ bool SetStartOnSystemStartup(bool fAutoStart) { return false; }
 
 void setClipboard(const QString& str)
 {
-    QApplication::clipboard()->setText(str, QClipboard::Clipboard);
+    QClipboard* clipboard = QApplication::clipboard();
-    QApplication::clipboard()->setText(str, QClipboard::Selection);
+    clipboard->setText(str, QClipboard::Clipboard);
+    if (clipboard->supportsSelection()) {
+        clipboard->setText(str, QClipboard::Selection);
+    }
 }
 
 fs::path qstringToBoostPath(const QString &path)