libressl defines SSL_OP_NO_SSLv2 and SSL_OP_NO_SSLv3 as 0x0
(thx Christian Heckendorf)
libressl matches ERR_remove_thread_state() signature from openssl 1.0.2
(libressl pretends that libressl is openssl version 2.0.0,
but openssl 1.1.0 changes signature of ERR_remove_thread_state())
libressl does not yet provide compatibility interfaces for the new
prototypes introduced in openssl 1.1.0, including
DH_set0_pqg() and DH_set_length()
remove OPENSSL_NO_KRB5 from build config (added in 5fab991b in 2005)
(define USE_OPENSSL_KERBEROS if required)
(Note: OPENSSL_NO_KRB5 removed in openssl 1.1.0)
Glenn Strauss
Stefan Bühler