patch 9.0.1307: setting 'formatoptions' with :let doesn't check for errors
Problem: Setting 'formatoptions' with :let doesn't check for errors.
Solution: Pass "errbuf" to set_string_option(). (Yegappan Lakshmanan,
closes #11974, closes #11972)
diff --git a/src/proto/optionstr.pro b/src/proto/optionstr.pro
index e75e3dc..d4f96be 100644
--- a/src/proto/optionstr.pro
+++ b/src/proto/optionstr.pro
@@ -8,7 +8,7 @@
void set_string_option_direct(char_u *name, int opt_idx, char_u *val, int opt_flags, int set_sid);
void set_string_option_direct_in_win(win_T *wp, char_u *name, int opt_idx, char_u *val, int opt_flags, int set_sid);
void set_string_option_direct_in_buf(buf_T *buf, char_u *name, int opt_idx, char_u *val, int opt_flags, int set_sid);
-char *set_string_option(int opt_idx, char_u *value, int opt_flags);
+char *set_string_option(int opt_idx, char_u *value, int opt_flags, char *errbuf);
char *did_set_string_option(int opt_idx, char_u **varp, char_u *oldval, char *errbuf, int opt_flags, int *value_checked);
int check_ff_value(char_u *p);
void save_clear_shm_value(void);