rktio: avoid nl_langinfo_l

Using `nl_langinfo_l` crashes the "unicode.rktl" test on Linux. I
don't know how `nl_langinfo_l` was being misused, but it's easy to
just avoid it.

racket/src/rktio/rktio_convert.c

@@ -356,10 +356,12 @@ static char *nl_langinfo_dup(rktio_t *rktio)
 {
   char *s;
 # if HAVE_CODESET
-#  ifdef RKTIO_USE_XLOCALE
-  s = nl_langinfo_l(CODESET, rktio->locale);
-#  else
+#  if defined(RKTIO_USE_XLOCALE)
+  locale_t old_l = uselocale(rktio->locale);
+#  endif
   s = nl_langinfo(CODESET);
+#  if defined(RKTIO_USE_XLOCALE)
+  uselocale(old_l);
 #  endif
 # else
   /* nl_langinfo doesn't work, so just make up something */