Jonathan Marler 93ac87c1bd Mark fstype argument to mount as optional
The fstype argument to the mount system call can be null.  To see an
example run "strace -e trace=mount unshare -m":

```
mount("none", "/", NULL, MS_REC|MS_PRIVATE, NULL) = 0
...
```
2022-07-05 15:04:31 -04:00
..
2021-11-09 07:08:27 -05:00
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