Fix a crasher that could happen when you run LLDB and evaluate an expression...

Fix a crasher that could happen when you run LLDB and evaluate an expression where the objective C runtime registers a helper function, and also have an Objective C or C++ exception breakpoint. When shutting down the process in Process::Finalize() we clear a STL collection class and that causes objects to be destroyed that could re-enter Process and cause it to try to iterate over that same collection class that is being destroyed.

Guard against this by setting a new "m_finalizing" flag that lets us know we are in the process of finalizing.

<rdar://problem/20369152>

llvm-svn: 233935