sdl: Initialization stubs

This reduces the number of CONFIG_SDL #ifdefs in vl.c.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

include/ui/console.h

@@ -422,8 +422,24 @@ void surface_gl_setup_viewport(ConsoleGLState *gls,
 #endif
 
 /* sdl.c */
+#ifdef CONFIG_SDL
 void sdl_display_early_init(int opengl);
 void sdl_display_init(DisplayState *ds, int full_screen, int no_frame);
+#else
+static inline void sdl_display_early_init(int opengl)
+{
+    /* This must never be called if CONFIG_SDL is disabled */
+    error_report("SDL support is disabled");
+    abort();
+}
+static inline void sdl_display_init(DisplayState *ds, int full_screen,
+                                    int no_frame)
+{
+    /* This must never be called if CONFIG_SDL is disabled */
+    error_report("SDL support is disabled");
+    abort();
+}
+#endif
 
 /* cocoa.m */
 void cocoa_display_init(DisplayState *ds, int full_screen);

vl.c

@@ -4251,11 +4251,10 @@ int main(int argc, char **argv, char **envp)
         early_gtk_display_init(request_opengl);
     }
 #endif
-#if defined(CONFIG_SDL)
     if (display_type == DT_SDL) {
         sdl_display_early_init(request_opengl);
     }
-#endif
+
     if (request_opengl == 1 && display_opengl == 0) {
 #if defined(CONFIG_OPENGL)
         error_report("OpenGL is not supported by the display");
@@ -4543,11 +4542,10 @@ int main(int argc, char **argv, char **envp)
     case DT_CURSES:
         curses_display_init(ds, full_screen);
         break;
-#if defined(CONFIG_SDL)
     case DT_SDL:
         sdl_display_init(ds, full_screen, no_frame);
         break;
-#elif defined(CONFIG_COCOA)
+#if defined(CONFIG_COCOA)
     case DT_COCOA:
         cocoa_display_init(ds, full_screen);
         break;