Adds test (Windows only) to Str.encode

Since that option is only available in Windows, I have added that test
with the optional code. Closes #459

S32-str/encode.t

@@ -11,7 +11,13 @@ is 'ab'.encode('ASCII').elems, 2, 'right length of Buf';
 ok ('ö'.encode('UTF-8') eqv utf8.new(195, 182)), 'encoding to UTF-8';
 is 'ab'.encode('UTF-8').elems, 2, 'right length of Buf';
 is 'a\nb'.encode('utf8').elems, 4, 'right length of Buf';
-ok 'a\nb'.encode('utf8') eqv utf8.new(97,0x5c,0x6e,98), 'Non-translation of \n';
+
+if $*DISTRO.is-win {
+    ok 'a\nb'.encode('utf8', :translate-nl) eqv utf8.new(97,0x0d,0x0a,98), 'Translation of \n in Windows environment';
+} else {
+    ok 'a\nb'.encode('utf8') eqv utf8.new(97,0x5c,0x6e,98), 'Non-translation of \n';
+}
+
 is 'ö'.encode('UTF-8')[0], 195, 'indexing a utf8 gives correct value (1)';
 is 'ö'.encode('UTF-8')[1], 182, 'indexing a utf8 gives correct value (1)';
 is '€‚ƒ„…†‡ˆ‰Š‹ŒŽ'.encode('windows-1252').values, (0x80,0x82..0x8c,0x8e), 'cp1252 encodes most C1 substitutes';