https://gitlab.synchro.net/main/sbbs/-/commit/f46582b9adaf2d303a591c17
Modified Files:
	src/syncterm/telnets.c
Log Message:
Use an atomic_bool instead of a mutext for telnets_active

This doesn't rely on implementation-defined behaviour.  I would like
to use call_once(), but I also want to be consistent with all the
other code, so use pthread_once() for now.
--- SBBSecho 3.23-Linux