patch 8.2.4804: expression in heredoc doesn't work for compiled function

Problem:    Expression in heredoc doesn't work for compiled function.
Solution:   Implement compiling the heredoc expressions. (Yegappan Lakshmanan,
            closes #10232)
diff --git a/src/proto/evalvars.pro b/src/proto/evalvars.pro
index 9e08f66..ab4320d 100644
--- a/src/proto/evalvars.pro
+++ b/src/proto/evalvars.pro
@@ -13,7 +13,7 @@
 int get_spellword(list_T *list, char_u **pp);
 void prepare_vimvar(int idx, typval_T *save_tv);
 void restore_vimvar(int idx, typval_T *save_tv);
-list_T *heredoc_get(exarg_T *eap, char_u *cmd, int script_get);
+list_T *heredoc_get(exarg_T *eap, char_u *cmd, int script_get, int vim9compile);
 void ex_var(exarg_T *eap);
 void ex_let(exarg_T *eap);
 int ex_let_vars(char_u *arg_start, typval_T *tv, int copy, int semicolon, int var_count, int flags, char_u *op);