gallium: Do not include offscreen winsys if glx is disabled

Offscreen winsys introduced in Mesa 22.2 depends on glx(dri) and libswkmsdri.

The error message is:
/usr/bin/ld: src/gallium/auxiliary/libgalliumvlwinsys.a.p/vl_vl_winsys_dri_vgem.c.o: in function `vl_vgem_drm_screen_create':
vl_winsys_dri_vgem.c:(.text.vl_vgem_drm_screen_create+0x28): undefined reference to `kms_dri_create_winsys'

Fixes: 31dcb396 (gallium/vl: Add software winsys and offscreen winsys)

Cc: mesa-stable
Signed-off-by: nyanmisaka <nst799610810@gmail.com>
Reviewed-by: Sil Vilerino <sivileri@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18843>

src/gallium/auxiliary/meson.build

@@ -475,7 +475,7 @@ endif
 
 if with_glx == 'xlib' or with_glx == 'gallium-xlib'
   files_libgalliumvlwinsys += files('vl/vl_winsys_xlib_swrast.c')
-else
+elif with_gallium_drisw_kms
   files_libgalliumvlwinsys += files('vl/vl_winsys_dri_vgem.c')
 endif
 

src/gallium/frontends/va/context.c

@@ -35,7 +35,9 @@
 #include "vl/vl_winsys.h"
 
 #include "va_private.h"
+#ifdef HAVE_DRISW_KMS
 #include "loader/loader.h"
+#endif
 
 #include <va/va_drmcommon.h>
 
@@ -146,12 +148,14 @@ VA_DRIVER_INIT_FUNC(VADriverContextP ctx)
          FREE(drv);
          return VA_STATUS_ERROR_INVALID_PARAMETER;
       }
+#ifdef HAVE_DRISW_KMS
       char* drm_driver_name = loader_get_driver_for_fd(drm_info->fd);
       if(drm_driver_name) {
          if (strcmp(drm_driver_name, "vgem") == 0)
             drv->vscreen = vl_vgem_drm_screen_create(drm_info->fd);
          FREE(drm_driver_name);
       }
+#endif
       if(!drv->vscreen)
          drv->vscreen = vl_drm_screen_create(drm_info->fd);
       break;