Fix Linux Host::GetCurrentThreadID() to return real tid (not pthread_t).
This fixes threadname logging (--thread-name)
Add "-t" to TestLogging.py script to enable threadsafe and disable threadname logging



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@187599 91177308-0d34-0410-b5e6-96231b3b80d8