Under certain conditions, we recompute the privacy consent

registrations. This can happen on thread startup or teardown, and

occasionally, two threads end up interfering with each other's state.
This happens because, when recomputing, an unregister is performed, and

on a blank registry this will trigger a registry population, which then

triggers a signal and another attempt at a recomputation, in the middle

of an existing one. If this happens in multiple threads, it compounds

the problem.
When this happens, we can end up triggering a double register of the new

consent requirements, which will crash.
We now surround all this with a threading lock, and check for this in

the signal handler to avoid triggering an extra recomputation.

Unit tests pass.
Consent requirements continue to work properly.