Update Travis configuration to run tests and build more configurations.

Update Travis configuration to run tests and build more configurations.

Install libcppunit-dev in order to be able to run the unit tests (at least the
non-GUI ones for now).

Also build in several configurations: shared/static, multilib/monolithic and
also STL. This should help to find problems appearing only in some specific
build variants.

Closes #15369.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74638 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775