initial import of mirage OS libraries
trim unused file
add gitignore
remove bad symlinks
delete config files accidentally committed
gitignore _config
include .a in build
[unix] port Unix to use Lwt_unix directly, and remove most of our custom stubs as a result
use a different linking strategy to fix the embedded rpath [untested]
include lwt.unix in depends
Revert "use a different linking strategy to fix the embedded rpath [untested]"

This reverts commit f98d919f8436955421e4e70ed49fef32c57e2509.
ccopt -> cclib
fix the binding compilation to use the right set of local vs runtime ccopts
add unix test for tuntap
trim unused var
sync with latest ocaml-build-skeleton
move the runtime into lib/ to avoid library path issues
do not double-pack the UNIX oS.cmx
restore the .cclib rule, which passes the contents directly to CC instead of via ocamlc.

The only difference is that ocamlc adds a -I<camllib> to the cc invocation, which is normally desirable, but not in the case of a Xen-crosscompile.  Therefore invoking cc directly is just more reliable in general.
remove the host OS checks completely, as they are unused