patch 8.2.3390: included xdiff code is outdated

Problem:    Included xdiff code is outdated.
Solution:   Sync with xdiff in git 2.33. (Christian Brabandt, closes #8431)
diff --git a/src/diff.c b/src/diff.c
index aea1c0e..7bdfa48 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -1095,7 +1095,7 @@
 
     emit_cfg.ctxlen = 0; // don't need any diff_context here
     emit_cb.priv = &diffio->dio_diff;
-    emit_cb.outf = xdiff_out;
+    emit_cb.out_line = xdiff_out;
     if (xdl_diff(&diffio->dio_orig.din_mmfile,
 		&diffio->dio_new.din_mmfile,
 		&param, &emit_cfg, &emit_cb) < 0)