Feature/warning request Pkcs11 is unimplemented

_wh_Server_HandlePkcs11Request is currently unimplemented and returns a null response size (see line 258 of wh_server.c). It otherwise doesn't provide any compile or runtime error to indicate the code isn't available. Would it be possible to throw an error on compile time if the call is present in the codebase? Longer term this would be a nice feature to have as it's available in WolfCrypt.