common: make this build with unbound 1.4.20

Common on currently used distros

src/common/dns_utils.cpp

@@ -230,7 +230,7 @@ DNSResolver::DNSResolver() : m_data(new DNSResolverData())
   if (use_dns_public)
   {
     for (const auto &ip: dns_public_addr)
-      ub_ctx_set_fwd(m_data->m_ub_context, ip.c_str());
+      ub_ctx_set_fwd(m_data->m_ub_context, string_copy(ip.c_str()));
     ub_ctx_set_option(m_data->m_ub_context, string_copy("do-udp:"), string_copy("no"));
     ub_ctx_set_option(m_data->m_ub_context, string_copy("do-tcp:"), string_copy("yes"));
   }

src/common/util.cpp

@@ -527,7 +527,10 @@ std::string get_nix_version_display_string()
   {
     ub_ctx *ctx = ub_ctx_create();
     if (!ctx) return false; // cheat a bit, should not happen unless OOM
-    ub_ctx_zone_add(ctx, "monero", "unbound"); // this calls ub_ctx_finalize first, then errors out with UB_SYNTAX
+    char *monero = strdup("monero"), *unbound = strdup("unbound");
+    ub_ctx_zone_add(ctx, monero, unbound); // this calls ub_ctx_finalize first, then errors out with UB_SYNTAX
+    free(unbound);
+    free(monero);
     // if no threads, bails out early with UB_NOERROR, otherwise fails with UB_AFTERFINAL id already finalized
     bool with_threads = ub_ctx_async(ctx, 1) != 0; // UB_AFTERFINAL is not defined in public headers, check any error
     ub_ctx_delete(ctx);