Thread-safety in log_backtrace()
On #9299 (moved), cypherpunks reports:
log_backtrace() is thread unsafe. If threads going to assert for the same time then calling of backtrace() from every thread going to fill the same cb_buf array.
Our options here are:
- Add a lock.
- Make the cb_buf field non-static, and hope that the stack won't mind.
The first option looks better, I think