Fix the following build failure with libressl >= 3.5.0:
tls.c:113:17: error: static declaration of 'OPENSSL_cleanup' follows non-static declaration
113 | static void OPENSSL_cleanup(void)
| ^~~~~~~~~~~~~~~
In file included from /home/thomas/autobuild/instance-3/output-1/host/mips-buildroot-linux-gnu/sysroot/usr/include/openssl/bio.h:69,
from /home/thomas/autobuild/instance-3/output-1/host/mips-buildroot-linux-gnu/sysroot/usr/include/openssl/evp.h:67,
from /home/thomas/autobuild/instance-3/output-1/host/mips-buildroot-linux-gnu/sysroot/usr/include/openssl/hmac.h:67,
from /home/thomas/autobuild/instance-3/output-1/host/mips-buildroot-linux-gnu/sysroot/usr/include/openssl/ssl.h:150,
from ../../../include/zbxcomms.h:65,
from tls.c:20:
/home/thomas/autobuild/instance-3/output-1/host/mips-buildroot-linux-gnu/sysroot/usr/include/openssl/crypto.h:565:6: note: previous declaration of 'OPENSSL_cleanup' with type 'void(void)'
565 | void OPENSSL_cleanup(void);
| ^~~~~~~~~~~~~~~
In file included from tls.c:20:
tls.c: In function 'zbx_log_ciphersuites':
../../../include/zbxcomms.h:222:75: error: invalid use of incomplete typedef 'SSL_CTX' {aka 'struct ssl_ctx_st'}