Fix Windows warnings : fix server_audit not to use my_win_open and Co functions.
Fix Windows warnings : fix server_audit not to use my_win_open and Co
functions.

There is no reason to export IO this functionality from server, if it can
be easily implemented with CRT.

Note: for the sake of compatibility, we do not use _open() on Windows,
but open file with CreateFile, with FILE_SHARE_DELETE flag,
so it can be renamed or deleted when open. Also atomic append flag is used.

natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2