Set st_fstype of stat on Solaris and Illumos OSes

[YohDeadfall]

Since rust-lang/libc#4145 is merged that FIXME is unblocked. I also decided to rename the method as it applies to Illumos too, so solarish seems more natural there.

[RalfJung]

This will require the libc version in rust'c library/Cargo.lock to be updated (and probably also in Miri's test_dependencies/Cargo.lock).

[RalfJung]

Actually never mind, the error is different than what I expected:

write_int on non-scalar type [i8; 16]

And indeed, looking at libc this is an array. You'll probably want to project to its first element and write 0 there; for a 0-terminated string, that should suffice.

[RalfJung]

This looks great, thanks! Please squash the commits, then we can land this. Please use the --keep-base flag when squashing so that the force-push diff is easier to review. Then write @rustbot ready after you pushed the squashed PR.

@rustbot author

[YohDeadfall]

@rustbot ready