fix build option issues; refine cmake

examples/qt_app_server/main_window.cc

@@ -0,0 +1,21 @@
+#include "examples/qt_app_server/main_window.h"
+
+#include <QDebug>
+
+MainWindow::MainWindow(Context* context, QWidget* parent)
+    : QMainWindow(parent) {
+  setWindowTitle("Qt App Server");
+
+#if 1
+  connect(context, &Context::SomeApiSignal, this, &MainWindow::OnSomeApiSignal);
+#else
+  // NOTE: Seems not necessary to use QueuedConnection (because we are using
+  // std::thread instead of QThread?).
+  connect(context, &Context::SomeApiSignal, this, &MainWindow::OnSomeApiSignal,
+          Qt::QueuedConnection);
+#endif
+}
+
+void MainWindow::OnSomeApiSignal(const QString& text) {
+  qDebug() << text;
+}