Create a private library directory (LIBPRIVATEDIR) for libraries which

Create a private library directory (LIBPRIVATEDIR) for libraries which
we don't want to expose but which can't or shouldn't be static.

To mark a library as private, define PRIVATELIB in its Makefile.  It
will be installed in LIBPRIVATEDIR, which is normally /usr/lib/private
(or /usr/lib32/private for 32-bit libraries on 64-bit platforms).

To indicate that a program or library depends on a private library,
define USEPRIVATELIB in its Makefile.  The correct version of
LIBPRIVATEDIR will be added to its run-time library search path.

Approved by:	re (blanket)