Add TestPrintObj.py to go with lang/objc/print-objc, which:

Test "print object" where another thread blocks the print object from making progress.

Set a breakpoint on the line in my_pthread_routine.  Then switch threads
to the main thread, and do print the lock_me object.  Since that will
try to get the lock already gotten by my_pthread_routime thread, it will
have to switch to running all threads, and that should then succeed.

llvm-svn: 133933