Fix for compile issues on Mac OS 14 (ARM)

[giffels]

This PR fixes the following issues when compiling gct on Mac OS 14 (ARM). However, I think these issues could be more general:

• <openssl/fips.h> is always included even if the underlying openssl version does not support FIPS_mode() anymore for example openssl 3.0.14 in my case
• connect_local_xsocket_path(path, sizeof(path)) needs (now?) length as second argument
• ssh-ecdsa.c and ssh-rsa.c require #include "ssh-pkcs11.h" if ENABLE_PKCS11 is true

Please, feel free to close the PR in case it is only affecting a not officially supported platform.

Thanks and best regards,
Manuel