Use atomic_bool instead of atomic_flag for doresizes

atomic_flag seems to be broken on Windows for clearing them outside the
thread they were tested and set in

src/qt/qt_rendererstack.cpp

@@ -44,6 +44,7 @@
 #endif
 
 extern "C" {
+#include <86box/86box.h>
 #include <86box/mouse.h>
 #include <86box/plat.h>
 #include <86box/video.h>
@@ -446,6 +447,7 @@ RendererStack::blitCommon(int x, int y, int w, int h)
 
 void RendererStack::closeEvent(QCloseEvent* event)
 {
+    if (cpu_thread_run == 0 || is_quit == 0) { event->accept(); return; }
     event->ignore();
     main_window->close();
 }