perl: Provide alternate definition of newSVpvn_utf8 for older Perl.

Commit 40fff10 uses newSVpvn_utf8.
This macro did not exist in Perl < 5.12, but we can use newSVpvn
instead.

Also update the associated test script:

- Don't use 'done_testing'.  Not supported by ancient Perl.

- Skip the tests entirely on ancient Perl.

generator/generator.ml

@@ -2351,6 +2351,11 @@ and generate_perl_xs () =
 #include <hivex.h>
 #include <inttypes.h>
 
+/* For Perl < 5.12 */
+#ifndef newSVpvn_utf8
+#define newSVpvn_utf8(a,b,u) newSVpvn((a),(b))
+#endif
+
 static SV *
 my_newSVll(long long val) {
 #ifdef USE_64_BIT_ALL

perl/t/130-special.t

@@ -7,8 +7,16 @@ BEGIN {
     binmode STDOUT, ':encoding(UTF-8)';
     binmode STDERR, ':encoding(UTF-8)';
 }
+
 use Test::More;
 
+# Old Perl hivex bindings cannot handle Unicode properly.
+if ($] < 5.012) {
+    plan skip_all => "Version of Perl is too old to handle Unicode";
+} else {
+    plan tests => 8;
+}
+
 use Win::Hivex;
 
 my $srcdir = $ENV{srcdir} || ".";
@@ -34,5 +42,3 @@ ok $value, 'value has been found';
 ok $node, q<'weird™' (node) has been found>;
 ($value) = grep { $h->value_key($_) eq 'symbols $£₤₧€' } $h->node_values($node);
 ok $value, q<'weird™\symbols $£₤₧€' (value) has been found>;
-
-done_testing;