Add critical section to filename function of  each file sink

Handling SPDLOG_PREVENT_CHILD_FD in tcp_sink

Adding SOCK_CLOEXEC to socket

Fixing bug in sink_it_ (bytes_sent not added to buffer)

tcp_sink implementation for fluentbit

Make tests support empty SPDLOG_EOL

adding additional log overload to prevent unnecessary fmt::format

Add eventlog_sink for logging to Windows Event Log (local only)

Properly handling SPDLOG_PREVENT_CHILD_FD

Removed check for posix version so that missing O_CLOEXEC leads to
compiler error.

Removed extra function since it hat no real purpose anymore.

Error behavior between Windows and Unix now equivalent.