update-glib-annotations: make it work with meson and drop autotools support
Clean up the code and make it work with meson. Assume a fixed build dir to make it less magic and so we can give better error messages.
This also removes all the include path logic because since c93dafe9 it no longer parses headers anyway and it wasn't doing anything with it.
Also tested on Windows.
Edited by Christoph Reiter