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_main.cpp

@@ -291,11 +291,12 @@ int main(int argc, char* argv[]) {
         /* If needed, handle a screen resize. */
         for (int i = 0; i < MONITORS_NUM; i++) {
             if (!monitors[i].target_buffer) continue;
-            if (!atomic_flag_test_and_set(&doresize_monitors[i]) && !video_fullscreen && !is_quit) {
+            if (atomic_load(&doresize_monitors[i]) == 1 && !video_fullscreen && !is_quit) {
                 if (vid_resize & 2)
                     plat_resize_monitor(fixed_size_x, fixed_size_y, i);
                 else
                     plat_resize_monitor(monitors[i].mon_scrnsz_x, monitors[i].mon_scrnsz_y, i);
+                atomic_store(&doresize_monitors[i], 0);
             }
         }