BUILD: ssl: replace SSL_CTX_get0_privatekey for openssl < 1.0.2

Commit 48a8332a introduce SSL_CTX_get0_privatekey in openssl-compat.h but
SSL_CTX_get0_privatekey access internal structure and can't be a candidate
to openssl-compat.h. The workaround with openssl < 1.0.2 is to use SSL_new
then SSL_get_privatekey.
diff --git a/include/proto/openssl-compat.h b/include/proto/openssl-compat.h
index 9b67109..ea92072 100644
--- a/include/proto/openssl-compat.h
+++ b/include/proto/openssl-compat.h
@@ -89,19 +89,6 @@
 }
 #endif
 
-#if (OPENSSL_VERSION_NUMBER < 0x10002000L) || defined(LIBRESSL_VERSION_NUMBER)
-/*
- * Functions introduced in OpenSSL 1.0.2 and not yet present in LibreSSL
- */
-EVP_PKEY *SSL_CTX_get0_privatekey(const SSL_CTX *ctx)
-{
-	if (ctx->cert != NULL)
-		return ctx->cert->key->privatekey;
-	else
-		return NULL;
-}
-#endif
-
 #if (OPENSSL_VERSION_NUMBER < 0x1010000fL) || defined(LIBRESSL_VERSION_NUMBER)
 /*
  * Functions introduced in OpenSSL 1.1.0 and not yet present in LibreSSL
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 8d38f28..7b1a0c9 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -1580,6 +1580,7 @@
 	SSL_CTX      *ssl_ctx = NULL;
 	X509         *newcrt  = NULL;
 	EVP_PKEY     *pkey    = NULL;
+	SSL          *tmp_ssl = NULL;
 	X509_NAME    *name;
 	const EVP_MD *digest;
 	X509V3_CTX    ctx;
@@ -1587,7 +1588,14 @@
 	int 	      key_type;
 
 	/* Get the private key of the default certificate and use it */
-	if (!(pkey = SSL_CTX_get0_privatekey(bind_conf->default_ctx)))
+#if (OPENSSL_VERSION_NUMBER >= 0x10002000L && !defined LIBRESSL_VERSION_NUMBER)
+	pkey = SSL_CTX_get0_privatekey(bind_conf->default_ctx);
+#else
+	tmp_ssl = SSL_new(bind_conf->default_ctx);
+	if (tmp_ssl)
+		pkey = SSL_get_privatekey(tmp_ssl);
+#endif
+	if (!pkey)
 		goto mkcert_error;
 
 	/* Create the certificate */
@@ -1704,6 +1712,7 @@
 	return ssl_ctx;
 
  mkcert_error:
+	if (tmp_ssl) SSL_free(tmp_ssl);
 	if (ssl_ctx) SSL_CTX_free(ssl_ctx);
 	if (newcrt)  X509_free(newcrt);
 	return NULL;