st/dri: Use fence extension in drisw.c

This is desirable for synchronization in virtual machines.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/state_trackers/dri/drisw.c

@@ -46,6 +46,7 @@
 #include "dri_screen.h"
 #include "dri_context.h"
 #include "dri_drawable.h"
+#include "dri_extensions.h"
 #include "dri_query_renderer.h"
 
 DEBUG_GET_ONCE_BOOL_OPTION(swrast_no_present, "SWRAST_NO_PRESENT", FALSE);
@@ -369,6 +370,7 @@ static const __DRIextension *drisw_screen_extensions[] = {
    &driTexBufferExtension.base,
    &dri2RendererQueryExtension.base,
    &dri2ConfigQueryExtension.base,
+   &dri2FenceExtension.base,
    NULL
 };