add a test for compile option match_unset_backref

src/tests/compile_opts.vtc

@@ -521,3 +521,31 @@ varnish v1 -errvcl {vmod pcre2 error: Cannot set locale lPb2PZDb4KcfbKJPSww1cm6o
 		new r = pcre2.regex("", locale="lPb2PZDb4KcfbKJPSww1cm6omvoF");
 	}
 }
+
+# match_unset_backref
+varnish v1 -vcl {
+	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
+	backend b { .host = "${bad_ip}"; }
+
+	sub vcl_init {
+		new r1 = pcre2.regex("(\3)(\1)(a)", match_unset_backref=true);
+		new r2 = pcre2.regex("(\3)(\1)(a)");
+	}
+
+	sub vcl_recv {
+		return(synth(200));
+	}
+
+	sub vcl_synth {
+		set resp.http.r1 = r1.match("cat");
+		set resp.http.r2 = r2.match("cat");
+	}
+}
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == "200"
+	expect resp.http.r1 == "true"
+	expect resp.http.r2 == "false"
+} -run