basic/log: always ignore errno from the enviornment (#8841)

basic/log: always ignore errno from the enviornment (#8841)

This extends the change done in b29f6480ec to other logging functions.

This actually fixes some bugs in callers of log_struct(), for example
config_parse_alias() called 'return log_syntax(..., 0, ...)' which could result
in a bogus non-zero return value.

Calls to log_object() and log_format_iovec() — which is only used by
server_driver_message() — appear correct.