Build: multiarch fixes

Use the libtool wrapper instead of /usr/bin/libtool. Update gi install
location for multiarch.
Use the libtool wrapper instead of /usr/bin/libtool. Update gi install location for multiarch.
Use the libtool wrapper instead of /usr/bin/libtool. Update gi install location for multiarch. 
Approved by: Iain Lane, David Barth
Releasing 1.18+15.04.20141110-0ubuntu1