This adds a unit test of importing a simple MathML file.
New smdllapi.hxx defines a macro SM_DLLPUBLIC to turn on
visibility of symbols required from a CppunitTest.

Change-Id: I4f72d7d8f2766751580e5bde7dac4870e8dad62a
Reviewed-on: https://gerrit.libreoffice.org/13861Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>