Fix missing-declaration errors in swig-gnc-optiondb-guile.cpp.

libgnucash/app-utils/gnc-optiondb.i

@@ -326,8 +326,9 @@ wrap_unique_ptr(GncOptionDBPtr, GncOptionDB);
  };
 
 %inline %{
-    SCM gnc_option_value(const GncOptionDBPtr& optiondb, const char* section,
-                         const char* name)
+    static SCM
+    gnc_option_value(const GncOptionDBPtr& optiondb, const char* section,
+                     const char* name)
     {
         auto db_opt = optiondb->find_option(section, name);
         if (!db_opt)
@@ -335,8 +336,9 @@ wrap_unique_ptr(GncOptionDBPtr, GncOptionDB);
         return GncOption_get_scm_value(&(db_opt->get()));
     }
 
-    SCM gnc_option_default_value(const GncOptionDBPtr& optiondb,
-                                 const char* section, const char* name)
+    static SCM
+    gnc_option_default_value(const GncOptionDBPtr& optiondb,
+                             const char* section, const char* name)
     {
         auto db_opt = optiondb->find_option(section, name);
         if (!db_opt)
@@ -344,8 +346,9 @@ wrap_unique_ptr(GncOptionDBPtr, GncOptionDB);
         return GncOption_get_scm_default_value(&(db_opt->get()));
     }
 
-    void gnc_set_option(const GncOptionDBPtr& optiondb, const char* section,
-                        const char* name, SCM new_value)
+    static void
+    gnc_set_option(const GncOptionDBPtr& optiondb, const char* section,
+                   const char* name, SCM new_value)
     {
         auto db_opt = optiondb->find_option(section, name);
         if (!db_opt)