C89 buildfix: Move variable declarations to block start in xmb_render()

Fixes C89 compliance issue where variables were declared mid-block:
- Move static retro_time_t last_scroll_time to function start
- Move static unsigned scroll_count to function start
- Move retro_time_t current_time to function start
- Move bool rapid_scroll to function start

This ensures all declarations are at the beginning of the block,
as required by the C89 standard.

Refs PR libretro#18828

Author: 龙虾机器人

menu/drivers/xmb.c

@@ -6847,6 +6847,12 @@ static void xmb_render(void *data,
    unsigned last                  = (unsigned)end;
    unsigned gfx_thumbnail_upscale_threshold = settings->uints.gfx_thumbnail_upscale_threshold;
    bool network_on_demand_thumbnails        = settings->bools.network_on_demand_thumbnails;
+   /* LOW-MEMORY FIX: Variables for rapid scroll detection
+    * Must be declared at block start for C89 compliance */
+   static retro_time_t last_scroll_time = 0;
+   static unsigned scroll_count = 0;
+   retro_time_t current_time;
+   bool rapid_scroll;
 
    if (!xmb)
       return;
@@ -7152,20 +7158,18 @@ static void xmb_render(void *data,
    {
       /* LOW-MEMORY FIX: Detect rapid scrolling and defer thumbnail loading
        * This prevents texture exhaustion on devices like Raspberry Pi and Switch */
-      static retro_time_t last_scroll_time = 0;
-      static unsigned scroll_count = 0;
-      retro_time_t current_time = cpu_features_get_time_usec();
-      
+      current_time = cpu_features_get_time_usec();
+
       /* Count scrolls within 100ms window */
       if (current_time - last_scroll_time < 100000)
          scroll_count++;
       else
          scroll_count = 1;
-      
+
       last_scroll_time = current_time;
-      
+
       /* If scrolling rapidly (>5 scrolls in 100ms), skip thumbnail loading */
-      bool rapid_scroll = (scroll_count > 5);
+      rapid_scroll = (scroll_count > 5);
 
       if (!rapid_scroll)
       {