Fix build with opaque structs in LibreSSL 3.5

Downloaded from OpenBSD ports:
http://cvsweb.openbsd.org/cgi-bin/cvsweb/ports/net/tor/patches/patch-src_lib_tls_x509_openssl_c?rev=1.2&content-type=text/x-cvsweb-markup

Patch series was sent upstream:
https://forum.torproject.net/t/tor-relays-openbsd-stable-net-tor-and-0-4-7-7/3244

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

Index: src/lib/tls/x509_openssl.c
--- a/src/lib/tls/x509_openssl.c.orig
+++ b/src/lib/tls/x509_openssl.c
@@ -329,7 +329,7 @@ tor_tls_cert_is_valid(int severity,
   cert_key = X509_get_pubkey(cert->cert);
   if (check_rsa_1024 && cert_key) {
     RSA *rsa = EVP_PKEY_get1_RSA(cert_key);
-#ifdef OPENSSL_1_1_API
+#if defined(OPENSSL_1_1_API) || defined(LIBRESSL_VERSION_NUMBER)
     if (rsa && RSA_bits(rsa) == 1024) {
 #else
     if (rsa && BN_num_bits(rsa->n) == 1024) {