patch 8.2.4615: mapping with escaped bar does not work in :def function

Problem:    Mapping with escaped bar does not work in :def function. (Sergey
            Vlasov)
Solution:   Do not remove the backslash. (closes #10002)
diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index 3be7471..40f2649 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -26,7 +26,7 @@
 char_u *skip_range(char_u *cmd_start, int skip_star, int *ctx);
 void ex_ni(exarg_T *eap);
 int expand_filename(exarg_T *eap, char_u **cmdlinep, char **errormsgp);
-void separate_nextcmd(exarg_T *eap);
+void separate_nextcmd(exarg_T *eap, int keep_backslash);
 char_u *skip_cmd_arg(char_u *p, int rembs);
 int get_bad_opt(char_u *p, exarg_T *eap);
 int ends_excmd(int c);