t/ascii_order.pl: Don't crash on early Perl EBCDICs

These would otherwise call an undefined function.  Just return instead
of doing that, which leads to incorrect results, but it's better than
crashing.

t/ascii_order.pl

@@ -4,7 +4,8 @@ ($)
                         # (which is the same as ASCII)
     my $string = shift;
 
-    return $string if ord("A") == 65;
+    return $string if ord("A") == 65
+                      || $] lt 5.007_003; # Doesn't work on early EBCDIC Perls
     my $output = "";
     for my $i (0 .. length($string) - 1) {
         $output .= chr(utf8::native_to_unicode(ord(substr($string, $i, 1))));