Fix a warning about unused variable
Fix a warning about unused variable

fil_ibd_create(): commit b731a5bcf2a0c86b6e31e4a99e3c632bb39a9c53
introduced a variable that was unused outside Windows. Use it
on all platforms.

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