Give every printf-like function restrict qualifiers

The format value has to be a string literal, every time.

Otherwise, you are not using these functions correctly. To reinforce this fact, I putrestrict over every non-contrib example of this I could find.

plugins/group_file/plugin_test.c

@@ -45,7 +45,7 @@ static void *group_handle;
 static struct sudoers_group_plugin *group_plugin;
 
 static int
-plugin_printf(int msg_type, const char *fmt, ...)
+plugin_printf(int msg_type, const char * restrict fmt, ...)
 {
     va_list ap;
     FILE *fp;