Unbreak the build on FreeBSD 11 which still has old OpenSSL in the base.

Pointy hat to:	danfe

www/squid3/files/patch-src_ssl_support.cc

 --- src/ssl/support.cc.orig	2018-07-15 20:46:55 UTC
 +++ src/ssl/support.cc
-@@ -2159,7 +2159,7 @@ remove_session_cb(SSL_CTX *, SSL_SESSION *sessionID)
+@@ -2159,7 +2159,11 @@ remove_session_cb(SSL_CTX *, SSL_SESSION *sessionID)
  }
  
  static SSL_SESSION *
 -get_session_cb(SSL *, unsigned char *sessionID, int len, int *copy)
-+get_session_cb(SSL *, const unsigned char *sessionID, int len, int *copy)
++get_session_cb(SSL *,
++#ifdef LIBRESSL_VERSION_NUMBER
++  const
++#endif
++  unsigned char *sessionID, int len, int *copy)
  {
      if (!SslSessionCache)
          return NULL;