fix Bug21211 : reworked test/api/multithreaded/test_listener_event_description.cpp to work properly on Linux/FreeBSD

Issue D5632 fixed an issue where linux would dump spurious output to tty on startup (due to a broadcast stop event). After the checkin, it was noticed on FreeBSD a unit test was now failing. On closer investigation I found the test was using the C++ API to launch an inferior while using an SBListener to monitor the public state changes. As on OSx, it was expecting to see:

eStateRunning
eStateStopped

On Linux/FreeBSD, there is an extra state change

eStateLaunching
eStateRunning
eStateStopped

I reworked the test to work for both cases and re-enabled the test of FreeBSD.

Differential Revision: http://reviews.llvm.org/D5837