<rdar://problem/13527167>

Partial fix for the above radar.

Call ThreadList::Clear() in the ThreadList destructor so if any other threads currently have the thread list mutex, we won't destroy the list for them while they are using it. ThreadList::Clear() takes the mutex and clears the thread list contents.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@178257 91177308-0d34-0410-b5e6-96231b3b80d8