make it possible to use --enable-fs more than once
make it possible to use --enable-fs more than once

Change add_fsname_auto() to join multiple --enable-fs options.

Note: "all" always wins, and "--enable-fs foo,all,bar" results
in fsauto_names = "all" too.

Signed-off-by: Oleg Nesterov <20b70f0af00562e63758b9ee42012ecc96c58590@redhat.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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