Force Voodoo blit

Certain applications using the Voodoo adapter stop blitting
when there's no activity (e.g mouse movement, animation).
This results in a black screen when events like window/full screen
transitions take place. Usually this can be fixed by
moving the mouse or with keyboard inout. This change forces
a blit to refresh the screen.

In addition, added critical sections since they are lighter
than mutexes.

src/include/86box/plat.h

@@ -142,6 +142,7 @@ extern void     ioctl_close(uint8_t id);
 typedef void thread_t;
 typedef void event_t;
 typedef void mutex_t;
+typedef void lightmutex_t;
 
 extern thread_t	*thread_create(void (*thread_func)(void *param), void *param);
 extern void	thread_kill(thread_t *arg);
@@ -157,6 +158,13 @@ extern void	thread_close_mutex(mutex_t *arg);
 extern int	thread_wait_mutex(mutex_t *arg);
 extern int	thread_release_mutex(mutex_t *mutex);
 
+#define LIGHT_MUTEX_DEFAULT_SPIN_COUNT 1024
+
+lightmutex_t *thread_create_light_mutex();
+lightmutex_t *thread_create_light_mutex_and_spin_count(unsigned int spin_count);
+int thread_wait_light_mutex(lightmutex_t *lightmutex);
+int thread_release_light_mutex(lightmutex_t *lightmutex);
+void thread_close_light_mutex(lightmutex_t *lightmutex);
 
 /* Other stuff. */
 extern void	startblit(void);

src/include/86box/vid_voodoo_common.h

@@ -489,6 +489,10 @@ typedef struct voodoo_t
         uint64_t time;
         int render_time[4];
 
+        int force_blit_count;
+        int can_blit;
+        lightmutex_t* force_blit_mutex;
+
         int use_recompiler;
         void *codegen_data;