Bringing if_clone with no modifications yet. Cloning devices allow resource allocation and resource release dynamically at runtime, for creating pseudo-device instances for each device type. Cloning interfaces are registered and deregistered using if_clone_attach and if_clone_detach, respectively.

* 'master' of github.com:cloudius-systems/osv:
  stop adding libm.so.6 from glibc to bootfs
  warn when we can't load ELF libraries from DT_NEEDED
  warn on unknown ELF section types
  fix up library pathnames in the ELF loader
  fix sem_wait
  add a __fprintf_chk implementation
  add popen/pclose stubs

Now that we actually look for DT_NEEDED libraries in the right place we
fail loading it because we don't support STT_GNU_IFUNC symbols.  But
by now we already have a feature complete libm implementation in our
tree so we don't actually need it anymore.

We want to look for /usr/lib/libfoo instead of /usr/liblibfoo

We need to use a spinlock to protect the semaphore waiting list as
the wakeups can deadlock otherwise.

Also make sure to only wait when we actually have to.

Found during python bringup.

no actual checking, but at least the code will work

* 'master' of github.com:cloudius-systems/osv:
  wire up the read and write methods for virtio-blk
  enable SMP locking in the filesystem code
  add mutex_init/destory and a static initializer

Before we had 2 layes of calls, one in the virtio ring layer and
another in the virtio-blk layer. There wasn't any reall need for that.
The change allows the virtio-vring code to call a callback that the virtio-blk
registers and execute it directly.

Since ->wake() can be called from an interrupt, we cannot to any allocations
there.

Resolved interdependencies later on.