patch 9.0.1262: the did_set_string_option function is too long

Problem:    The did_set_string_option function is too long.
Solution:   Split off functionality to individual functions.  (Yegappan
            Lakshmanan, Lewis Russell, closes #11904)

src/proto/gui_xim.pro

@@ -1,6 +1,6 @@
 /* gui_xim.c */
-int set_imactivatefunc_option(void);
-int set_imstatusfunc_option(void);
+char *set_imactivatefunc_option(void);
+char *set_imstatusfunc_option(void);
 void free_xim_stuff(void);
 int set_ref_in_im_funcs(int copyID);
 void im_set_active(int active);

src/proto/insexpand.pro

@@ -44,11 +44,11 @@ int ins_compl_bs(void);
 void ins_compl_addleader(int c);
 void ins_compl_addfrommatch(void);
 int ins_compl_prep(int c);
-int set_completefunc_option(void);
+char *set_completefunc_option(void);
 void set_buflocal_cfu_callback(buf_T *buf);
-int set_omnifunc_option(void);
+char *set_omnifunc_option(void);
 void set_buflocal_ofu_callback(buf_T *buf);
-int set_thesaurusfunc_option(void);
+char *set_thesaurusfunc_option(void);
 int set_ref_in_insexpand_funcs(int copyID);
 void f_complete(typval_T *argvars, typval_T *rettv);
 void f_complete_add(typval_T *argvars, typval_T *rettv);

src/proto/ops.pro

@@ -17,7 +17,7 @@ void block_prep(oparg_T *oap, struct block_def *bdp, linenr_T lnum, int is_del);
 void op_addsub(oparg_T *oap, linenr_T Prenum1, int g_cmd);
 void clear_oparg(oparg_T *oap);
 void cursor_pos_info(dict_T *dict);
-int set_operatorfunc_option(void);
+char *set_operatorfunc_option(void);
 void free_operatorfunc_option(void);
 int set_ref_in_opfunc(int copyID);
 void do_pending_operator(cmdarg_T *cap, int old_col, int gui_yank);

src/proto/quickfix.pro

@@ -15,7 +15,7 @@ void ex_cclose(exarg_T *eap);
 void ex_copen(exarg_T *eap);
 void ex_cbottom(exarg_T *eap);
 linenr_T qf_current_entry(win_T *wp);
-int qf_process_qftf_option(void);
+char *qf_process_qftf_option(void);
 int grep_internal(cmdidx_T cmdidx);
 void ex_make(exarg_T *eap);
 int qf_get_size(exarg_T *eap);

src/proto/tag.pro

@@ -1,5 +1,5 @@
 /* tag.c */
-int set_tagfunc_option(void);
+char *set_tagfunc_option(void);
 void free_tagfunc_option(void);
 int set_ref_in_tagfunc(int copyID);
 void set_buflocal_tfu_callback(buf_T *buf);