User functions provided by recent LibreSSL versions

At least on OpenBSD, this enables new APIs out of the box provided by
LibreSSL 2.7.1 and higher.

From Jeremie Courreges-Anglas <jca@openbsd.org>.

src/socket.c

@@ -40,7 +40,8 @@
 # include <openssl/ssl.h>
 # include <openssl/err.h>
 # include <openssl/x509v3.h>
-# if OPENSSL_VERSION_NUMBER < 0x10100000L
+# if OPENSSL_VERSION_NUMBER < 0x10100000L \
+	|| (defined(LIBRESSL_VERSION_NUMBER) && LIBRESSL_VERSION_NUMBER >= 0x2070100fL)
 #  define X509_OBJECT_get0_X509(o) ((o)->data.x509)
 #  define X509_STORE_get0_objects(o) ((o)->objs)
 # endif