putw is supposed to return 0 (not the value written) on success

this is not a standard but it's the traditional behavior and it's more
useful because the caller can reliably detect errors.

src/stdio/putw.c

@@ -3,5 +3,5 @@
 
 int putw(int x, FILE *f)
 {
-	return fwrite(&x, sizeof x, 1, f) ? x : EOF;
+	return (int)fwrite(&x, sizeof x, 1, f)-1;
 }