hide purely dependency-triggering functions in stdio __toread & __towrite

src/stdio/__toread.c

@@ -13,7 +13,7 @@ int __toread(FILE *f)
 	return (f->flags & F_EOF) ? EOF : 0;
 }
 
-void __toread_needs_stdio_exit()
+hidden void __toread_needs_stdio_exit()
 {
 	__stdio_exit_needed();
 }

src/stdio/__towrite.c

@@ -17,7 +17,7 @@ int __towrite(FILE *f)
 	return 0;
 }
 
-void __towrite_needs_stdio_exit()
+hidden void __towrite_needs_stdio_exit()
 {
 	__stdio_exit_needed();
 }