wafsamba: allow certain public libraries to be forced to be private

wafsamba: allow certain public libraries to be forced to be private

This will help installations where the Samba4 libraries must be used but
the main system is not using the system libs that would normally
be installed.  This in particular impacts on libwbclient, which is a
core dep, but is different to that used by the rest of a Samba 3.x based
system.

Use eg:  ./configure --private-libraries=wbclient

Andrew Bartlett

Autobuild-User: Andrew Bartlett <abartlet@samba.org>
Autobuild-Date: Fri Apr 20 03:27:22 CEST 2012 on sn-devel-104