This lets other bits of userspace expose these various definitions too.
In particular, this will be used by libprocstat so it can stop defining
_KERNEL.
The function prototypes surely won't be useful in other contexts, but
the various types are, and it's not worth hiding the prototypes unless
they end up causing issues, but so long as they aren't called they
shouldn't be a problem.
Note the MAKEFS define continues to exist, but only for use in
newfs_msdos, as those sources are reused by makefs with some changed
behaviour.
Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D50718
b61239ef83