Fix build with LibreSSL

Index: src/SWIG/_lib.i
--- src/SWIG/_lib.i.orig
+++ src/SWIG/_lib.i
@@ -21,7 +21,7 @@
 
 %{
 /* OpenSSL 1.0.2 copmatbility shim */
-#if OPENSSL_VERSION_NUMBER < 0x10002000L
+#if OPENSSL_VERSION_NUMBER < 0x10002000L || defined(LIBRESSL_VERSION_NUMBER)
 typedef void (*OPENSSL_sk_freefunc)(void *);
 typedef void *(*OPENSSL_sk_copyfunc)(const void *);
 typedef struct stack_st OPENSSL_STACK;