libtool/depdemo

This is depdemo, an example package that uses GNU libtool with an
Automake-generated environment to build many interdependent libraries
and a test program.

There are four libraries: l1, l2, l3 and l4.
l1 depends on nothing.
l2 depends on l1.
l3 depends on l1 and l2.
l4 depends on l3 and libm.

The test program uses l1, l2 and l4.