loongarch: add SDL_FillSurfaceRect4LSX opt

(cherry picked from commit dc5b136930)

CMakeLists.txt

@@ -901,11 +901,13 @@ if(SDL_ASSEMBLY)
         set_property(SOURCE
             "${SDL3_SOURCE_DIR}/src/video/yuv2rgb/yuv_rgb_lsx.c"
             "${SDL3_SOURCE_DIR}/src/video/SDL_blit_A.c"
+            "${SDL3_SOURCE_DIR}/src/video/SDL_fillrect.c"
             APPEND PROPERTY COMPILE_OPTIONS "-mlsx")
 
         set_property(SOURCE
             "${SDL3_SOURCE_DIR}/src/video/yuv2rgb/yuv_rgb_lsx.c"
             "${SDL3_SOURCE_DIR}/src/video/SDL_blit_A.c"
+            "${SDL3_SOURCE_DIR}/src/video/SDL_fillrect.c"
             PROPERTY SKIP_PRECOMPILE_HEADERS 1)
         set(HAVE_LSX TRUE)
       endif()