sys: Use libtool for pthreaded library

sys: Use libtool for pthreaded library

Create a pthreaded version of libsys.a, called liboafs_sys.a

On AIX, the sys library is special because it includes references to
two syscall stubs - lpioctl and lsetpag. This means that we can't link
the library with -no-undefined, as the references to these stubs are
only resolved at run time.

Change-Id: Iaae5923fe4eec7bc3f006e29df4e26e4ba8e5418
Reviewed-on: http://gerrit.openafs.org/8061
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>