patch 9.1.0071: Need a diff() Vim script function

Problem:  Need a diff() Vim script function
Solution: Add the diff() Vim script function using the
          xdiff internal diff library, add support for
          "unified" and "indices" mode.
          (Yegappan Lakshmanan)

fixes: #4241
closes: #12321

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/diff.pro b/src/proto/diff.pro
index d14907e..9c34dcf 100644
--- a/src/proto/diff.pro
+++ b/src/proto/diff.pro
@@ -30,4 +30,5 @@
 linenr_T diff_lnum_win(linenr_T lnum, win_T *wp);
 void f_diff_filler(typval_T *argvars, typval_T *rettv);
 void f_diff_hlID(typval_T *argvars, typval_T *rettv);
+void f_diff(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */