toy-font-face was checking that cairo_toy_font_face_get_family returned ""
which is CAIRO_FONT_FAMILY_DEFAULT when the freetype font backend is the
default. However, when other font backends are the default the returned family
is different. Therefore, instead of checking for "", we check for the appropriate
string depending on the backend.
Avoid calling libtool to link every single test case, by building just one
binary from all the sources.
This binary is then given the task of choosing tests to run (based on user
selection and individual test requirement), forking each test into its own
process and accumulating the results.
