Remove a deadlock condition. A bit of explanation is needed: When calling

ThreadCancel in Host::WillTerminate g_monitor_thread may be blocked on a call
to pthread_cond_wait (for example, line 640).  Now, by default, when a 
cancellation request is serviced g_monitor_thread will again own the mutex
guarding the condition variable it was waiting on.  This causes the call to 
SetValue in Host::WillTerminate to hit a deadlock.

The call to SetValue does not appear to be needed, so removing it solves
the issue.

Patch from Stephen Wilson.

llvm-svn: 109228