adjust iswalnum to admit tail call to iswalpha

use of || forces the caller to boolean-normalize the result of
iswalpha to 0 or 1, requiring code after the call returns and thus
precluding a tail call.

since this isn't actually needed, don't write it that way.

src/ctype/iswalnum.c

@@ -2,7 +2,8 @@
 
 int iswalnum(wint_t wc)
 {
-	return iswdigit(wc) || iswalpha(wc);
+	if (iswdigit(wc)) return 1;
+	return iswalpha(wc);
 }
 
 int __iswalnum_l(wint_t c, locale_t l)