drisw: fix build without dri3

commit 1887368df4 ("glx/sw: check for modifier support in the kopper path")
added dri3_priv.h header and dri3_check_multibuffer() function in drisw that
can be build without dri3.

Commit 4477139ec2 added a guard around dri3_check_multibuffer()
function but not around dri3_priv.h header.

Add HAVE_DRI3 guard around dri3_priv.h header.

Fixes: 1887368df4 ("glx/sw: check for modifier support in the kopper path")

v2: Remove the guard around dri3_check_multibuffer() function.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Antoine Coutant <antoine.coutant@smile.fr>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27478>

src/glx/drisw_glx.c

@@ -32,7 +32,9 @@
 #include <dlfcn.h>
 #include "dri_common.h"
 #include "drisw_priv.h"
+#ifdef HAVE_DRI3
 #include "dri3_priv.h"
+#endif
 #include <X11/extensions/shmproto.h>
 #include <assert.h>
 #include <vulkan/vulkan_core.h>