[PATCH v4 2/5] fs: Add fchmodat2()

[Christian Brauner]

> > I think it'd be much neater to do the conversion of AT_ flags here and
> > pass 0 as a flags argument for all of the wrappers (this is how most of
> > the other xyz(), fxyz(), fxyzat() syscall wrappers are done IIRC).

I've fixed that up in-tree.