Native Windows: Eina: Resolve bad comparison while using windows strerror_s

Native Windows: Eina: Resolve bad comparison while using windows strerror_s

`strerror_s` is the windows alternative of `strerror_r` used by EFL.

`strerror_s` never return the error code with the message as
`strerror_r` does, because of that, while comparing the first 14
characters of `Unknown error ` to the message from unknown code 4096
(`Unknown error`) they were accusing being different - in UNIX this
works because the message returned is `Unknown error 4096`.
This error was noticeable at `eina_error_test_failures` test case.

This Diff adds the error code to the message in case of an `Unknown
error`, making the windows implementation compliant with UNIX.

Reviewed-by: Vincent Torri <vincent.torri@gmail.com>
Reviewed-by: Wander Lairson Costa <wander.lairson@gmail.com>
Reviewed-by: Stefan Schmidt <stefan@datenfreihafen.org>
Differential Revision: https://phab.enlightenment.org/D12033