Fix build with libressl

It got another feature of openssl implemented, which broke this

CMakeLists.txt

@@ -82,6 +82,20 @@ endmacro()
 tristate_option(OPENSSL "Support SSL")
 if(WANT_OPENSSL)
 	find_package(OpenSSL ${TRISTATE_OPENSSL_REQUIRED})
+
+	if(OPENSSL_FOUND)
+		# SSL_SESSION was made opaque in OpenSSL 1.1.0;
+		# LibreSSL gained that function later too.
+		# TODO: maybe remove this check at some point, and stop supporting old
+		# libssl versions
+		function(check_SSL_SESSION_get0_cipher)
+			set(CMAKE_REQUIRED_LIBRARIES ${OPENSSL_LIBRARIES})
+			set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
+			check_cxx_symbol_exists(SSL_SESSION_get0_cipher openssl/ssl.h
+				HAVE_SSL_SESSION_get0_cipher)
+		endfunction()
+		check_SSL_SESSION_get0_cipher()
+	endif()
 endif()
 set(HAVE_LIBSSL "${OPENSSL_FOUND}")
 

include/znc/zncconfig.h.cmake.in

@@ -31,6 +31,7 @@
 #define HAVE_PTHREAD 1
 #cmakedefine HAVE_THREADED_DNS 1
 #cmakedefine HAVE_LIBSSL 1
+#cmakedefine HAVE_SSL_SESSION_get0_cipher 1
 #cmakedefine HAVE_IPV6 1
 #cmakedefine HAVE_ZLIB 1
 #cmakedefine HAVE_I18N 1

modules/schat.cpp

@@ -25,8 +25,7 @@
 #include <znc/User.h>
 #include <znc/IRCNetwork.h>
 
-#if !defined(OPENSSL_VERSION_NUMBER) || defined(LIBRESSL_VERSION_NUMBER) || \
-    OPENSSL_VERSION_NUMBER < 0x10100007
+#ifndef HAVE_SSL_SESSION_get0_cipher
 /* SSL_SESSION was made opaque in OpenSSL 1.1.0, cipher accessor was added 2
 weeks before the public release.
 See openssl/openssl@e92813234318635639dba0168c7ef5568757449b. */