comerr: Convert to using libtool

comerr: Convert to using libtool

Convert the libafs_comerr library so that it uses libtool.

comerr uses a pthread lock to protect the error tables, so it needs
to be built as both an LWP, and a pthread library (previously, we've
just built it as LWP, which is probably broken on some platforms, as
it won't define -D_REENTRANT)

libafscom_err.a remains as the LWP variant, and all pthreaded code is
modified to use the libtool liboafs_comerr.la library.

Change-Id: Id421cc97ad8681b42af7a5eb3cb512e1e1ce9a90
Reviewed-on: http://gerrit.openafs.org/8054
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: Derrick Brashear <shadow@your-file-system.com>