xlib: Fixes compiling on linux

configure command line:
meson ../.. -Dglx=xlib -Dosmesa=true

link error:
virgl_screen.c.o: in function `virgl_is_video_format_supported':
/mnt/c/work/xemu/mesa/build/windows-wsl2/../../src/gallium/drivers/virgl/virgl_screen.c:885: undefined reference to `vl_video_buffer_is_format_supported'

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7545

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Ack-by: Eric Engestrom <eric@igalia.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19258>

src/gallium/auxiliary/vl/vl_stubs.c

@@ -108,6 +108,11 @@ vl_video_buffer_create_ex2(struct pipe_context *pipe,
    return NULL;
 }
 
+void
+vl_video_buffer_destroy(struct pipe_video_buffer *buffer)
+{
+   assert(0);
+}
 
 /*
  * vl_mpeg12_bitstream stubs

src/gallium/targets/libgl-xlib/meson.build

@@ -49,7 +49,7 @@ libgl = shared_library(
   link_args : [ld_args_bsymbolic, ld_args_gc_sections, gallium_xlib_ld_args],
   link_depends : gallium_xlib_link_depends,
   link_with : [
-    libxlib, libws_xlib, libglapi_static,
+    libgalliumvl_stub, libxlib, libws_xlib, libglapi_static,
     libgallium, libmesa, gallium_xlib_link_with,
   ],
   dependencies : [dep_x11, dep_thread, dep_clock, dep_unwind, driver_swrast, driver_virgl, driver_asahi],