Would be cool to find a POSIX tag file somewhere.
Most tags files are [here](https://wiki.geany.org/tags/start) and there is a win32 but no *ix :(
Have a look at the miscellaneous [scripts](https://github.com/geany/geany/tree/master/scripts) some of which generate the standard global tags files. Modifying one of those might be the way to go.