Handle `lockfile` functions for mutual exclusion

[sim642]

Related to a couple of *_unlocked functions from the list, turns out there are flockfile, ftrylockfile and funlockfile, which treat a FILE as a mutex. No idea, if anyone uses them, but I guess it wouldn't hurt to also consider those for mutual exclusion.

Originally posted by @sim642 in https://github.com/goblint/analyzer/issues/723#issuecomment-1117621513