Windows does not have syslog, so the server_audit plugin does not try to build syslog support on Windows. Instead, it just defines the syslog-related functions as noops on Windows:
server_audit_output_type=SYSLOG can still be set on Windows:
Since the syslog functions are defined as noops on Windows, this output type will not do anything.
It seems like it would be better to not allow server_audit_output_type=SYSLOG on Windows.