LibreSSL doesn't define OPENSSL_VERSION, use LIBRESSL_VERSION_TEXT instead

[paveljanik]

OpenBSD is using LibreSSL by default instead of openssl. The build ends with

CXX      libbitcoin_server_a-init.o
In file included from addrman.h:14:0,
                 from init.cpp:12:
init.cpp: In function 'bool AppInit2(boost::thread_group&, CScheduler&)':
init.cpp:1095:61: error: 'OPENSSL_VERSION' was not declared in this scope
     LogPrintf("Using OpenSSL version %s\n", OpenSSL_version(OPENSSL_VERSION));
                                                             ^

This change adds LIBRESSL_VERSION_TEXT macrocheck and adds conditionals before these macros. If none is defined, nothing is printed at all.

Fixes #7515.
Fixes #7447.

[luke-jr]

utACK a0a17b3

[laanwj]

utACK