QEMU fails to honor O_TMPFILE

When making a call like

  open("/tmp", O_TMPFILE | O_RDWR);

under QEMU, we ged -EISDIR.

Under any kernel 3.11 or later, we are supposed to get an unnamed file in /tmp. In case the filesystem for /tmp does not support unnamed files, we are supposed to get EOPNOTSUPP.

[I don't know the QEMU version, since this happened in a system I don't have access to]