s4-waf: support the use of system libraries

s4-waf: support the use of system libraries

distros can set --bundled-libraries=NONE to force use of all system
libraries. If the right version isn't found then configure will fail.

Users may choose which libraries to use from the system, and which to
use bundled libs. The default is to try system libs, and use them if
their version matches the one in the source tree.