Use the following for openssl 1.1+:
- X509_getm_notBefore over X509_get_notBefore
- X509_getm_notAfter over X509_get_notAfter
- use OPENSSL_VERSION_NUMBER over SSLeay()
- add missing headers
Refs: openssl/openssl@0b7347effe
LibreSSL 2.7 implements OpenSSL 1.1 API except for BIO_get_init()
See also: https://bugs.freebsd.org/226900
Signed-off-by: Bernard Spil <brnrd@FreeBSD.org>
Closes: #617 (cherry-pick)