ccan: make it a grouping library.

ccan: make it a grouping library.

Andrew Bartlett pointed out that making CCAN a non-library will break
the build in a different way in future: when two separate private
libraries start using the same CCAN module, the symbol duplicate
detection will fire (since private libaries don't use any symbol
hiding).  That doesn't happen yet, but it will surely happen
eventually.

So, for now at least, we build as a private library again.  This
unfortunately means the top-level build creates a libccan.so, which
contains all the ccan modules whether you need them or not.  Given the
size of the library, I don't think this is a win.  But it's simple.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Autobuild-User(master): Rusty Russell <rusty@rustcorp.com.au>
Autobuild-Date(master): Sat Jun 30 11:19:04 CEST 2012 on sn-devel-104