xapian-bridge C port

endlessm/eos-sdk#2463
It looks to me like `glib.mk` is meant to be copied into other projects (see for example the lines at the top that say "uncomment this if not building GLib") but it looks like it does quite a lot more than we currently need, and requires reorganizing our Makefile. So it's fine with me to just define the variables and not include `glib.mk`. We can reconsider that if we enable lcov for this project.