SSL: reasonable version for LibreSSL. LibreSSL defines OPENSSL_VERSION_NUMBER to 0x20000000L, but uses an old API derived from OpenSSL at the time LibreSSL forked. As a result, every version check we use to test for new API elements in newer OpenSSL versions requires an explicit check for LibreSSL. To reduce clutter, redefine OPENSSL_VERSION_NUMBER to 0x1000107fL if LibreSSL is used. The same is done by FreeBSD port of LibreSSL.